diff --git a/src/include/units/physical/dimensions.h b/src/include/units/physical/dimensions.h
index eaec5174..496d626a 100644
--- a/src/include/units/physical/dimensions.h
+++ b/src/include/units/physical/dimensions.h
@@ -122,6 +122,12 @@ struct dim_inductance : derived_dimension<Child, U, exp<F, 1>, exp<I, -1>> {};
 template<typename Child, Unit U, DimensionOf<dim_resistance> R>
 struct dim_conductance : derived_dimension<Child, U, exp<R, -1>> {};
 
+// template<typename Child, Unit U, DimensionOf<dim_time> T>
+// struct dim_radioactivity : derived_dimension<Child, U, exp<T, -1>> {};
+
+template<typename Child, Unit U, DimensionOf<dim_time> T, DimensionOf<dim_substance> M>
+struct dim_catalytic_activity : derived_dimension<Child, U, exp<T, -1>, exp<M, 1>> {};
+
 }  // namespace physical
 
 template<typename T>
@@ -190,13 +196,19 @@ concept Pressure = physical::QuantityOf<T, physical::dim_pressure>;
 template<typename T>
 concept MagneticInduction = physical::QuantityOf<T, physical::dim_magnetic_induction>;
 
-template <typename T>
+template<typename T>
 concept MagneticFlux = physical::QuantityOf<T, physical::dim_magnetic_flux>;
 
-template <typename T>
+template<typename T>
 concept Inductance = physical::QuantityOf<T, physical::dim_inductance>;
 
-template <typename T>
+template<typename T>
 concept Conductance = physical::QuantityOf<T, physical::dim_inductance>;
 
+// template<typename T>
+// concept Radioactivity = physical::QuantityOf<T, physical::dim_radioactivity>;
+
+template<typename T>
+concept CatalyticActivity = physical::QuantityOf<T, physical::dim_catalytic_activity>;
+
 }  // namespace units
diff --git a/src/include/units/physical/si/catalytic_activity.h b/src/include/units/physical/si/catalytic_activity.h
new file mode 100644
index 00000000..8e7f2fc9
--- /dev/null
+++ b/src/include/units/physical/si/catalytic_activity.h
@@ -0,0 +1,60 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#pragma once
+
+#include <units/physical/dimensions.h>
+#include <units/physical/si/substance.h>
+#include <units/physical/si/time.h>
+#include <units/physical/si/prefixes.h>
+#include <units/quantity.h>
+
+namespace units::si {
+
+struct katal : named_unit<katal, "kat", prefix> {};
+struct nanokatal : prefixed_unit<nanokatal, nano, katal> {};
+
+struct enzyme_unit : named_scaled_unit<enzyme_unit, "U", prefix, ratio<1, 60, -6>, katal> {};
+
+struct dim_catalytic_activity : physical::dim_catalytic_activity<dim_catalytic_activity, katal, dim_time, dim_substance> {};
+
+template<Unit U, Scalar Rep = double>
+using catalytic_activity = quantity<dim_catalytic_activity, U, Rep>;
+
+inline namespace literals {
+
+// kat
+constexpr auto operator"" q_kat(unsigned long long l) { return catalytic_activity<katal, std::int64_t>(l); }
+constexpr auto operator"" q_kat(long double l) { return catalytic_activity<katal, long double>(l); }
+
+// nkat
+constexpr auto operator"" q_nkat(unsigned long long l) { return catalytic_activity<nanokatal, std::int64_t>(l); }
+constexpr auto operator"" q_nkat(long double l) { return catalytic_activity<nanokatal, long double>(l); }
+
+// U
+constexpr auto operator"" q_U(unsigned long long l) { return catalytic_activity<enzyme_unit, std::int64_t>(l); }
+constexpr auto operator"" q_U(long double l) { return catalytic_activity<enzyme_unit, long double>(l); }
+
+}  // namespace literals
+
+}  // namespace units::si
+
diff --git a/test/unit_test/runtime/fmt_units_test.cpp b/test/unit_test/runtime/fmt_units_test.cpp
index 1b298a8e..d1c2bd70 100644
--- a/test/unit_test/runtime/fmt_units_test.cpp
+++ b/test/unit_test/runtime/fmt_units_test.cpp
@@ -43,6 +43,7 @@
 #include "units/physical/si/magnetic_flux.h"
 #include "units/physical/si/inductance.h"
 #include "units/physical/si/conductance.h"
+#include "units/physical/si/catalytic_activity.h"
 #include "units/format.h"
 #include <catch2/catch.hpp>
 
@@ -229,6 +230,12 @@ TEST_CASE("fmt::format on synthesized unit symbols", "[text][fmt]")
     CHECK(fmt::format("{}", 1q_nS) == "1 nS");
   }
 
+  SECTION("catalytic activity")
+  {
+    CHECK(fmt::format("{}", 1q_kat) == "1 kat");
+    CHECK(fmt::format("{}", 1q_U) == "1 U");
+  }
+
   SECTION("addition with common ratio")
   {
     CHECK(fmt::format("{}", 1q_in + 1q_yd) == "37 in");
diff --git a/test/unit_test/static/si_test.cpp b/test/unit_test/static/si_test.cpp
index 6720b60f..6ebd86a7 100644
--- a/test/unit_test/static/si_test.cpp
+++ b/test/unit_test/static/si_test.cpp
@@ -44,6 +44,7 @@
 #include <units/physical/si/magnetic_flux.h>
 #include <units/physical/si/inductance.h>
 #include <units/physical/si/conductance.h>
+#include <units/physical/si/catalytic_activity.h>
 #include <utility>
 
 namespace {
@@ -236,6 +237,11 @@ static_assert(millisiemens::symbol == "mS");
 static_assert(microsiemens::symbol == basic_symbol_text("µS", "uS"));
 static_assert(nanosiemens::symbol == "nS");
 
+// catalytic activity
+
+static_assert(1q_kat == 1q_mol / 1q_s);
+static_assert(1'000'000q_U == 1q_mol / 1q_min);
+
 /* ************** DERIVED DIMENSIONS IN TERMS OF BASE UNITS **************** */
 
 // velocity