The crystal of a mixed ligand complex of praseodymium perchlorate with imidazole (C₃H₄N₂) and DL-α-alanine (C₃H₇NO₂) was synthesized and characterized. The empirical formula of the crystal was determined to be [Pr(C₃H₇NO₂)₂(C₃H₄N₂)(H₂O)](ClO₄)₃ by FT-IR spectrum, chemical analysis and elemental analysis. The enthalpy of reaction of PrCl₃•6H₂O(s)＋2C₃H₇NO₂(s)＋C₃H₄N₂(s)＋3NaClO₄(s)＝[Pr(C₃H₇NO₂)₂(C₃H₄N₂)(H₂O)](ClO₄)₃(s)＋3NaCl(s)＋5H₂O(l) in 2.0 mol•L^－1 HCl solvents was determined to beΔ_rH_m^?＝(39.26±0.11) kJ•mol^－1 by a solution-reaction isoperibol calorimeter at T＝(298.150±0.001) K. According to Hess’s Law, the standard molar enthalpy of formation of the title complex was derived, Δ_fH_m^?{[Pr(C₃H₇NO₂)₂(C₃H₄N₂)(H₂O)](ClO₄)₃(s), 298.150 K}＝(－2424.2±3.3) kJ•mol^－1. The non-isothermal thermal decomposition kinetics of the complex in flow atmosphere of high purity nitrogen (99.99%) was studied by TG-DTG techniques. The non-isothermal kinetics parameters were analyzed by means of differential (Achar-Brindley-shap and Kissinger method) and integral (Satava-Sastak and Coats-Redfern methods) methods, respectively. The apparent activation energy of the thermal decomposition reaction was obtained to give: E＝108.9 kJ•mol^－1, and the kinetic equation may be expressed as: dα/dt＝2(5.90×10⁸/3)(1－α)[－ln(1－α)]^－1exp(－108.9×10³/RT).

Key words: complex of rare earth, solution-reaction calorimetry, standard enthalpy of formation, TG-DTG technique, thermal decomposition kinetics