diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index c88b2607cddf5cfc83d2676e9aa805d10afc062c..fe5d75d78aa003025d0265856557694dadbcfb83 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,26 @@
+*   Add subsec to `ActiveSupport::TimeWithZone#inspect`.
+
+    Before:
+
+        Time.at(1498099140).in_time_zone.inspect
+        # => "Thu, 22 Jun 2017 02:39:00 UTC +00:00"
+        Time.at(1498099140, 123456780, :nsec).in_time_zone.inspect
+        # => "Thu, 22 Jun 2017 02:39:00 UTC +00:00"
+        Time.at(1498099140 + Rational("1/3")).in_time_zone.inspect
+        # => "Thu, 22 Jun 2017 02:39:00 UTC +00:00"
+
+    After:
+
+        Time.at(1498099140).in_time_zone.inspect
+        # => "Thu, 22 Jun 2017 02:39:00 UTC +00:00"
+        Time.at(1498099140, 123456780, :nsec).in_time_zone.inspect
+        # => "Thu, 22 Jun 2017 02:39:00.12345678 UTC +00:00"
+        Time.at(1498099140 + Rational("1/3")).in_time_zone.inspect
+        # => "Thu, 22 Jun 2017 02:39:00 1/3 UTC +00:00"
+
+
+    *akinomaeni*
+
 *   Calling `ActiveSupport::TaggedLogging#tagged` without a block now returns a tagged logger.
 
     ```ruby
diff --git a/activesupport/lib/active_support/time_with_zone.rb b/activesupport/lib/active_support/time_with_zone.rb
index 49b874b6a6a4f1481193b436122a3aaa05bfd724..097d7be8f24299c72361646b9c1c40af4157c277 100644
--- a/activesupport/lib/active_support/time_with_zone.rb
+++ b/activesupport/lib/active_support/time_with_zone.rb
@@ -139,7 +139,7 @@ def zone
     #
     #   Time.zone.now.inspect # => "Thu, 04 Dec 2014 11:00:25 EST -05:00"
     def inspect
-      "#{time.strftime('%a, %d %b %Y %H:%M:%S')} #{zone} #{formatted_offset}"
+      "#{time.strftime('%a, %d %b %Y %H:%M:%S')}#{formatted_subsec_with_delimiter} #{zone} #{formatted_offset}"
     end
 
     # Returns a string of the object's date and time in the ISO 8601 standard
@@ -581,5 +581,26 @@ def wrap_with_time_zone(time)
           time
         end
       end
+
+      def formatted_subsec
+        return "" if subsec.zero?
+
+        if (1_000_000_000 % subsec.denominator).zero?
+          format("%09d", subsec * 1_000_000_000).sub(/0+$/, "")
+        else
+          subsec.to_s
+        end
+      end
+
+      def formatted_subsec_with_delimiter
+        subsec = formatted_subsec
+        if subsec.empty?
+          subsec
+        elsif subsec.include?("/")
+          " #{subsec}"
+        else
+          ".#{subsec}"
+        end
+      end
   end
 end
diff --git a/activesupport/test/core_ext/time_with_zone_test.rb b/activesupport/test/core_ext/time_with_zone_test.rb
index 02205ac47d6141de8a1b5a764a0658536d65fbda..3831b6558d53ffdd53a2dff50bf91c6edb0f51ba 100644
--- a/activesupport/test/core_ext/time_with_zone_test.rb
+++ b/activesupport/test/core_ext/time_with_zone_test.rb
@@ -115,6 +115,18 @@ def test_strftime_with_escaping
 
   def test_inspect
     assert_equal "Fri, 31 Dec 1999 19:00:00 EST -05:00", @twz.inspect
+
+    nsec          = Time.utc(1986, 12, 12, 6, 23, 00, Rational(1, 1000))
+    nsec          = ActiveSupport::TimeWithZone.new(nsec, @time_zone)
+    assert_equal "Fri, 12 Dec 1986 01:23:00.000000001 EST -05:00", nsec.inspect
+
+    handred_nsec  = Time.utc(1986, 12, 12, 6, 23, 00, Rational(100, 1000))
+    handred_nsec  = ActiveSupport::TimeWithZone.new(handred_nsec, @time_zone)
+    assert_equal "Fri, 12 Dec 1986 01:23:00.0000001 EST -05:00", handred_nsec.inspect
+
+    one_third_sec = Time.utc(1986, 12, 12, 6, 23, 00, Rational(1000000, 3))
+    one_third_sec = ActiveSupport::TimeWithZone.new(one_third_sec, @time_zone)
+    assert_equal "Fri, 12 Dec 1986 01:23:00 1/3 EST -05:00", one_third_sec.inspect
   end
 
   def test_to_s
@@ -717,7 +729,7 @@ def test_beginning_of_year
 
   def test_end_of_year
     assert_equal "Fri, 31 Dec 1999 19:00:00 EST -05:00", @twz.inspect
-    assert_equal "Fri, 31 Dec 1999 23:59:59 EST -05:00", @twz.end_of_year.inspect
+    assert_equal "Fri, 31 Dec 1999 23:59:59.999999999 EST -05:00", @twz.end_of_year.inspect
   end
 
   def test_beginning_of_month
@@ -727,7 +739,7 @@ def test_beginning_of_month
 
   def test_end_of_month
     assert_equal "Fri, 31 Dec 1999 19:00:00 EST -05:00", @twz.inspect
-    assert_equal "Fri, 31 Dec 1999 23:59:59 EST -05:00", @twz.end_of_month.inspect
+    assert_equal "Fri, 31 Dec 1999 23:59:59.999999999 EST -05:00", @twz.end_of_month.inspect
   end
 
   def test_beginning_of_day
@@ -737,7 +749,7 @@ def test_beginning_of_day
 
   def test_end_of_day
     assert_equal "Fri, 31 Dec 1999 19:00:00 EST -05:00", @twz.inspect
-    assert_equal "Fri, 31 Dec 1999 23:59:59 EST -05:00", @twz.end_of_day.inspect
+    assert_equal "Fri, 31 Dec 1999 23:59:59.999999999 EST -05:00", @twz.end_of_day.inspect
   end
 
   def test_beginning_of_hour
@@ -751,7 +763,7 @@ def test_end_of_hour
     utc = Time.utc(2000, 1, 1, 0, 30)
     twz = ActiveSupport::TimeWithZone.new(utc, @time_zone)
     assert_equal "Fri, 31 Dec 1999 19:30:00 EST -05:00", twz.inspect
-    assert_equal "Fri, 31 Dec 1999 19:59:59 EST -05:00", twz.end_of_hour.inspect
+    assert_equal "Fri, 31 Dec 1999 19:59:59.999999999 EST -05:00", twz.end_of_hour.inspect
   end
 
   def test_beginning_of_minute
@@ -765,7 +777,7 @@ def test_end_of_minute
     utc = Time.utc(2000, 1, 1, 0, 30, 10)
     twz = ActiveSupport::TimeWithZone.new(utc, @time_zone)
     assert_equal "Fri, 31 Dec 1999 19:30:10 EST -05:00", twz.inspect
-    assert_equal "Fri, 31 Dec 1999 19:30:59 EST -05:00", twz.end_of_minute.inspect
+    assert_equal "Fri, 31 Dec 1999 19:30:59.999999999 EST -05:00", twz.end_of_minute.inspect
   end
 
   def test_since