The aim of the study was to investigate the phytochemical constituents present in Caesalpinia bonducella seeds kernel (CBSK) extract using Gas chromatography and mass spectrum analysis and evaluate the antioxidant activity. Twenty-nine phytochemical compounds identified Gas chromatography and mass spectrum analysis. The important phytoconstituents were 3-O-Methyl-d-glucose -12.39 (16.89%), 17-(1-acetoxy-ethyl)-10,13-dimethyl-3-oxo2,3,8,9,10,11,12,13,14,15,16,17-dodecahedron-1H-cyclopenta [a] phenanthrene-11-yl(ester) (17.03%), Acetic acid, α-D-Glucopyranoside, O-α-D-glucopyranosyl -(1. fwdarw.3) -β-D- fructofuranosyl-9.41 (13.92%), 5,16,20-Pregnatriene-3beta,20-diol diacetate-29.08 (7.22%), 8,11,14-Eicosatrienoic acid, (Z,Z,Z) -22.92 (6.05%). Antioxidant activity was expressed as ascorbic acid corresponding antioxidant capacity (AEAC). Gas chromatography and mass spectrum helps to predict the structure and formula of phytocompounds in Caesalpinia bonducella seeds kernel which can be used as herbal medicines for various ailments and Caesalpinia bonducella seeds kernel has good antioxidant activity.