Abstract: A new compound, barium nicotinate trihydrate, was synthesized by the method of room temperature solid phase synthesis and ball grinder. FTIR, chemical and elemental analyses, and X-ray powder diffraction techniques were applied to characterize the structure and composition of the complex. Low-temperature heat capacities of the solid coordination compound were measured by a precision automated adiabatic calorimeter over the temperature range from78 to 400 K. A phase transition process occurred in the temperature range of 312-332 K in the heat capacity curve, and the peak temperature, molar enthalpy and entropy of the solid-to-solid phase transition of the complex were determined to be as follows: Ttrs=(327.097±1.082) K, ⊿trsHm=(16.793±0.084) kJ·mol-1 and ⊿trsSm=(51.340±0.164) J·K-1·mol-1. The experimental values of the molar heat capacities in the temperature regions of 78-311 K and 333 -400 K were respectively fitted to two polynomial equations. The polynomial fitted values of the molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature of 298.15 K were calculated and tabulated at an interval of 5 K. In accordance with Hess law, a thermochemical cycle was designed, the reaction enthalpy of the solid phase reaction was determined as ⊿rH0m
=-(84.12±0.38) kJ·mol-1, and the standard molar enthalpy of formation of the complex was calculated as ⊿fH0m[Ba(Nic)2·3H2O(s)]=-(2115.13±1.90) kJ·mol-1 by using an isoperibol solution-reaction calorimeter.