The heat capacities of 3 - (2,2-dichloroethenyl) -2,2-dimethylcyclopropanecarboxylic acid ( a racemic mixture,molar ratio of cis-/trans-structure is 35/65) in a temperature range from 78 to 389 K were measured with a precise automatic adiabatic calorimeter. The sample was prepared with a purity of 98.75% ( molar 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, of the acid were determined to be ( 331.48 ± 0.03 ) K, ( 16. 321 ± 0.031 ) kJ/mol,and (49.24 ± 0.19) J/( K·mol), respectively. The thermodynamic functions of the sample, HT - H298.15, ST -S298.15 and GT - G298.15, were reported at a temperature intervals of 5 K. The thermal decomposition of the sample was studied using thermogravimetric (TG) analytic technique, the thermal decomposition starts at ca. 418 K and ends at ca. 544 K, the maximum decomposition rate was obtained at 510 K. The order of reaction, preexponential factor and activation energy are n =0.23, A =7. 3 × 107 min -1, E =70.64 KJ/mol, respectively.