The Gibbs free energy of formation of Er2Ru2O7(s) has been determined using solid-state electrochemical technique employing oxide ion conducting electrolyte. The reversible electromotive force (e.m.f.) of the following solid-state electrochemical cell has been measured: (-)Pt/{Er2O3(s) + Er2Ru2O7(s) + Ru(s)}//CSZ//O-2(P(O-2) = 21.21 kPa)/Pt(+). The Gibbs free energy of formation of Er2Ru2O7(s) from elements in their standard state, calculated by the least squares regression analysis of the data obtained in the present study, can be given by: {Delta(f)G degrees(Er2Ru2O7, s)/(kJ.mol(-1)) +/- 2.2} = -2517.3 + 0.6099.(T/K); (934.6 <= T/K <= 1236.3). Standard molar heat capacity C-p,C-m degrees(T) of Er2Ru2O7(s) was measured using a heat flux type differential scanning calorimeter (DSC) in two different temperature ranges, from 129 K to 296 K and 307 K to 845 K. The heat capacity in the higher temperature range was fitted into a polynomial expression and can be represented by: C-p,C-m degrees(Er2Ru2O7, s, T)(J.K-1.mol(-1)) = 293.88 + 2.39710(-2)T(K) -54.7471710(5)/T-2(K); (307 <= T(K)<= 845). The heat capacity of Er2Ru2O7(s), was used along with the data obtained from the oxide electrochemical cell to calculate the standard enthalpy and entropy of formation of the compound at 298.15 K. (C) 2013 Elsevier BM. All rights reserved.