Ba3CuO4(s) is one of the important compounds as a proton conducting electrolyte which form due to interaction of BaO and CuO. In the present study, Ba3CuO4(s) has been synthesized by solid state route and the Gibbs energy of formation and heat capacity has been experimentally measured by Knudsen Effusion Mass Spectrometer and differential scanning calorimeter. The Delta G(f) (Ba3CuO4, s, T) and C-p degrees, (Ba3CuO4, s, T) is obtained as per given equations: Delta G(f) (Ba3CuO4, s, T) +/- 7/kJ mol(-1) = -1888 + 0.4229.(T/K) C-p degrees (Ba3CuO4, s, T)(JK(-1 )mol(-1)) +/- 6 = 211 + 0.0274.(T/K) - 3039600.(T/K)(-2) The binary phase diagram of BaO-CuO system has been calculated based on the Gibbs energy minimization method. Using the experimental thermodynamic data, isothermal chemical potential diagram of Ba-Cu-C-O system with different axial parameter and ternary phase diagram of Ba (s) - Cu (s) - O-2 (g) system has been calculated in order to study the thermodynamic stability and coexisting phases of Ba3CuO4(s).