The interaction of butyltin compounds which include monobutyltin trichloride (MBT), dibutyltin dichloride (DBT) and tributyltin chloride (TBT) with bovine serum albumin (BSA) was studied by UV and CD spectra. The results showed that the interaction were dual. Butyltin compounds can not onlybehaves the coordinate action of butyltin ion with BSA but also does the hydrophobic actions of butyl group to BSA which will cause the change of the shape of BSA and decrease of α-spiral content. The effects of different...