The heat capacities of fenpropathrin in the temperature range from 80 to 400 K were measured with a precise automatic adiabatic calorimeter. The fenpropathrin sample was prepared with the purity of 0.9916 mole fraction. A solid—liquid fusion phase transition was observed in the experimental temperature range. The melting point, Tm, enthalpy and entropy of fusion, fusHm, fusSm, were determined to be 322.48±0.01 K, 18.57±0.29 kJ mol–1 and 57.59±1.01 J mol–1 K–1, respectively. The thermodynamic functions of fenpropathrin, H(T)—H(298.15), S(T)—S(298.15) and G(T)—G(298.15), were reported with a temperature interval of 5 K. The TG analysis under the heating rate of 10 K min–1 confirmed that the thermal decomposition of the sample starts at ca. 450 K and terminates at ca. 575 K. The maximum decomposition rate was obtained at 558 K. The purity of the sample was determined by a fractional melting method.