diff --git a/src/HttpServer.cc b/src/HttpServer.cc
index 5ce17b46..e58e800f 100644
--- a/src/HttpServer.cc
+++ b/src/HttpServer.cc
@@ -96,7 +96,7 @@ Config::Config()
       session_option(nullptr), data_ptr(nullptr), padding(0), num_worker(1),
       header_table_size(-1), port(0), verbose(false), daemon(false),
       verify_client(false), no_tls(false), error_gzip(false),
-      early_response(false) {
+      early_response(false), hexdump(false) {
   nghttp2_option_new(&session_option);
   nghttp2_option_set_recv_client_preface(session_option, 1);
 }
@@ -426,6 +426,11 @@ int Http2Handler::read_clear() {
     if (nread == 0) {
       return -1;
     }
+
+    if (get_config()->hexdump) {
+      util::hexdump(stdout, buf.data(), nread);
+    }
+
     rv = nghttp2_session_mem_recv(session_, buf.data(), nread);
     if (rv < 0) {
       if (rv != NGHTTP2_ERR_BAD_PREFACE) {
@@ -548,6 +553,11 @@ int Http2Handler::read_tls() {
     }
 
     auto nread = rv;
+
+    if (get_config()->hexdump) {
+      util::hexdump(stdout, buf.data(), nread);
+    }
+
     rv = nghttp2_session_mem_recv(session_, buf.data(), nread);
     if (rv < 0) {
       if (rv != NGHTTP2_ERR_BAD_PREFACE) {
diff --git a/src/HttpServer.h b/src/HttpServer.h
index 5b8de7ef..8ca52775 100644
--- a/src/HttpServer.h
+++ b/src/HttpServer.h
@@ -71,6 +71,7 @@ struct Config {
   bool no_tls;
   bool error_gzip;
   bool early_response;
+  bool hexdump;
   Config();
   ~Config();
 };
diff --git a/src/nghttp.cc b/src/nghttp.cc
index 10b7e712..bfed0372 100644
--- a/src/nghttp.cc
+++ b/src/nghttp.cc
@@ -79,7 +79,7 @@ Config::Config()
       timeout(0.), window_bits(-1), connection_window_bits(-1), verbose(0),
       null_out(false), remote_name(false), get_assets(false), stat(false),
       upgrade(false), continuation(false), no_content_length(false),
-      no_dep(false), dep_idle(false) {
+      no_dep(false), dep_idle(false), hexdump(false) {
   nghttp2_option_new(&http2_option);
   nghttp2_option_set_peer_max_concurrent_streams(http2_option,
                                                  peer_max_concurrent_streams);
@@ -1048,6 +1048,10 @@ int HttpClient::on_connect() {
 }
 
 int HttpClient::on_read(const uint8_t *data, size_t len) {
+  if (config.hexdump) {
+    util::hexdump(stdout, data, len);
+  }
+
   auto rv = nghttp2_session_mem_recv(session, data, len);
   if (rv < 0) {
     std::cerr << "[ERROR] nghttp2_session_mem_recv() returned error: "
@@ -2421,6 +2425,8 @@ Options:
               Don't send content-length header field.
   --no-dep    Don't send dependency based priority hint to server.
   --dep-idle  Use idle streams as anchor nodes to express priority.
+  --hexdump   Output  incoming traffic  in  `hexdump  -C` format.   If
+              SSL/TLS is used, decrypted data are used.
   --version   Display version information and exit.
   -h, --help  Display this help and exit.
 
@@ -2461,6 +2467,7 @@ int main(int argc, char **argv) {
         {"no-dep", no_argument, &flag, 7},
         {"dep-idle", no_argument, &flag, 8},
         {"trailer", required_argument, &flag, 9},
+        {"hexdump", no_argument, &flag, 10},
         {nullptr, 0, nullptr, 0}};
     int option_index = 0;
     int c = getopt_long(argc, argv, "M:Oab:c:d:gm:np:r:hH:vst:uw:W:",
@@ -2647,6 +2654,10 @@ int main(int argc, char **argv) {
         util::inp_strlower(config.trailer.back().name);
         break;
       }
+      case 10:
+        // hexdump option
+        config.hexdump = true;
+        break;
       }
       break;
     default:
diff --git a/src/nghttp.h b/src/nghttp.h
index dc45fa6d..7466e099 100644
--- a/src/nghttp.h
+++ b/src/nghttp.h
@@ -84,6 +84,7 @@ struct Config {
   bool no_content_length;
   bool no_dep;
   bool dep_idle;
+  bool hexdump;
 };
 
 enum class RequestState { INITIAL, ON_REQUEST, ON_RESPONSE, ON_COMPLETE };
diff --git a/src/nghttpd.cc b/src/nghttpd.cc
index 275a4827..f2c14f48 100644
--- a/src/nghttpd.cc
+++ b/src/nghttpd.cc
@@ -145,6 +145,8 @@ Options:
               include pseudo header field  (header field name starting
               with ':').  The  trailer is sent only if  a response has
               body part.  Example: --trailer 'foo: bar'.
+  --hexdump   Output  incoming traffic  in  `hexdump  -C` format.   If
+              SSL/TLS is used, decrypted data are used.
   --version   Display version information and exit.
   -h, --help  Display this help and exit.
 
@@ -176,6 +178,7 @@ int main(int argc, char **argv) {
         {"dh-param-file", required_argument, &flag, 4},
         {"early-response", no_argument, &flag, 5},
         {"trailer", required_argument, &flag, 6},
+        {"hexdump", no_argument, &flag, 7},
         {nullptr, 0, nullptr, 0}};
     int option_index = 0;
     int c = getopt_long(argc, argv, "DVb:c:d:ehn:p:va:", long_options,
@@ -284,6 +287,10 @@ int main(int argc, char **argv) {
         util::inp_strlower(config.trailer.back().name);
         break;
       }
+      case 7:
+        // hexdump option
+        config.hexdump = true;
+        break;
       }
       break;
     default:
diff --git a/src/util.cc b/src/util.cc
index 1b6ffb74..ab948d7e 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -1046,6 +1046,70 @@ std::string make_hostport(const char *host, uint16_t port) {
   return hostport;
 }
 
+#define NGHTTP2_SPACES                                                         \
+  "                                                                          " \
+  "     "
+
+namespace {
+void hexdump8(FILE *out, const uint8_t *first, const uint8_t *last) {
+  auto stop = std::min(first + 8, last);
+  for (auto k = first; k != stop; ++k) {
+    fprintf(out, "%02x ", *k);
+  }
+  /* each byte needs 3 spaces (2 hex value and space).  we have extra
+     space after 8 bytes */
+  fprintf(out, "%.*s", static_cast<int>((first + 8 - stop) * 3 + 1),
+          NGHTTP2_SPACES);
+}
+} // namespace
+
+void hexdump(FILE *out, const uint8_t *src, size_t len) {
+  if (len == 0) {
+    return;
+  }
+  size_t buflen = 0;
+  auto repeated = false;
+  std::array<uint8_t, 16> buf{};
+  auto end = src + len;
+  auto i = src;
+  for (;;) {
+    auto nextlen = std::min(static_cast<ptrdiff_t>(16), end - i);
+    if (nextlen == buflen &&
+        std::equal(std::begin(buf), std::begin(buf) + buflen, i)) {
+      /* as long as adjacent 16 bytes block are the same, we just
+         print single '*'. */
+      if (!repeated) {
+        repeated = true;
+        fwrite("*\n", 2, 1, out);
+      }
+      i += nextlen;
+      continue;
+    }
+    repeated = false;
+    fprintf(out, "%08lx", static_cast<unsigned long>(i - src));
+    if (i == end) {
+      fwrite("\n", 2, 1, out);
+      break;
+    }
+    fwrite("  ", 2, 1, out);
+    hexdump8(out, i, end);
+    hexdump8(out, i + 8, std::max(i + 8, end));
+    fwrite("|", 1, 1, out);
+    auto stop = std::min(i + 16, end);
+    buflen = stop - i;
+    auto p = buf.data();
+    for (; i != stop; ++i) {
+      *p++ = *i;
+      if (0x20 <= *i && *i <= 0x7e) {
+        fwrite(i, 1, 1, out);
+      } else {
+        fwrite(".", 1, 1, out);
+      }
+    }
+    fwrite("|\n", 2, 1, out);
+  }
+}
+
 } // namespace util
 
 } // namespace nghttp2
diff --git a/src/util.h b/src/util.h
index b30eb707..f20624d5 100644
--- a/src/util.h
+++ b/src/util.h
@@ -612,6 +612,9 @@ std::string format_duration(const std::chrono::microseconds &u);
 // and "]".  If |port| is 80 or 443, port part is omitted.
 std::string make_hostport(const char *host, uint16_t port);
 
+// Dumps |src| of length |len| in the format similar to `hexdump -C`.
+void hexdump(FILE *out, const uint8_t *src, size_t len);
+
 } // namespace util
 
 } // namespace nghttp2