The heat capacity of ammonium hexachlororuthenate, (NH4)(2)RuCl6, was measured over the temperature range 5 <= T/K <= 325 using adiabatic calorimetry. Our results show that a structural phase transition is not present. However, an anomalous increase in the heat capacity C-p,C-m occurs in the region 70 <= T/K <= 105 and the heat capacity reaches its maximum at T = (93.5 +/- 0.1) K. The molar entropy change associated with this increase amounts to Delta S-m = (0.465 +/- 0.006) R. Standard molar thermodynamic functions are presented at selected temperatures from 5 K to 325 K. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.