Carboxylesterases are hydrolases which catalyze the hydrolysis of various types of esters. Carboxylesterase from the seeds of Jatropha curcas has been purified to homogeneity using ammonium sulfate fractionation, CM-cellulose chromatography, Sephadex G-100 chromatography and preparative polyacrylamide gel electrophoresis (PAGE). The homogeneity of the purified enzyme was confirmed by PAGE, iso-electrofocusing and SDS-PAGE. The molecular weight of the purified enzyme was determined by both gel-permeation chromatography on Sephadex G-150 and SDS-PAGE. The molecular weight determined by Sephadex G-150 chromatography and SDS-PAGE both in the presence and absence of 2-mercaptoethanol was 31 kDa. The isoelectric point of the purified enzyme was found to be 8.9. JCSE-I (J. curcas seed esterase-I) was classified as carboxylesterase on the basis of substrate and inhibitor specificity. The K(m) of JCSE-I with 1-naphthyl acetate, 1-naphthyl propionate, 1-naphthyl butyrate and 2-naphthyl acetate as substrates were found to be 0.0,794, 0.0,658, 0.0,567 and 0.1 mM, respectively. The enzyme exhibited an optimum temperature of 45 °C and an optimum pH of 6.5. The enzyme was stable up to 15 min at 65 °C. The enzyme was resistant towards carbamates (carbaryl and eserine sulfate) and sulphydryl inhibitors (p-chloromercuricbenzoate, PCMB) and inhibited by organophosphates (dichlorvos, parathion and phosphamidon).