To better predict the bioaccumulation potential of chemicals without animal tests, the biotransformation rates of a series of alkylphenols were measured using liver S9 fractions from rainbow trout (RT-S9). Due to steric hindrance, the reaction rate of some chemicals with the tert-butyl moiety was slower than the QSAR-based prediction. Based on the observed rate constants and the unbound fractions of substrates in the RT-S9 reaction system, the bioconcentration factors (BCFs) were estimated by a previously proposed model. Calculated BCF values were well consistent with the bioaccumulation potential determined by the animal tests.