Phytochemical investigations on the chloroform soluble fraction of the whole plant of Withania somnifera led to the isolation of 20b hydroxy-1-oxo(22R) witha-2,5,24 trienolide 1, (20R, 22R-14a, 20a)-dihydroxy-1-oxowitha-2,5,16,24 tetraenolide 2, and (20R, 22R)-1 oxo-5a, 8b-dihydroxywitha-6a, 7b-epoxide-2,24-dienolide (withasomilide) 3. The structures of these compounds were confirmed through spectral studies in comparison with data in the literature. These isolated compounds (1–3) exhibited potent inhibition against a-glucosidase with IC50 values of 98.60, 38.20, and 40.65 lg/ml respectively.