The catalytic properties of bovine serum albumin (BSA) have been studied rather extensively. The protein has shown catalytic activities toward a variety of reactions in aqueous media. However, there appears to be no reports of reactions catalyzed exclusively in organic media. In this study, we report the catalytic property of BSA on the isomerization of 1,2-benzisoxazole in an organic solvent. Kinetics were performed using a continuous flow system in a spectrophotometer at 330 rim. The catalysis showed a Michaells-Menten behavior with an estimated catalytic, efficiency (k(cat)/K-M) of 8.77 M-1S-1. The influence of water content and inhibitors was also studied. The activity of BSA in acetonitrile is approximately 20% of that in water under similar conditions. Inhibition studies show that the active site may be the pyridoxal binding site involving Lys-220.