The metabolites of butylbenzyl phthalate in mice urine were identified by HPLC-MS(n). After the analysis of speculated metabolites and standard sample by HPLC-UV and the second full mass scanning (MS2), we find six metabolites: phthalic acid, benzoyl glycocoll, monobutyl phthalate, benzyl phthalate, glucuronyl-monobutyl phthalate, glucuronyl-benzyl phthalate. We deduced metabolic approach of butyl benzyl phthalate in vivo was that butyl benzyl phthalate hydrolyzed into the phthalic acid, monobutyl phthalate and benzyl phthalate. Partial phthalic acid became into benzoic acid by decarboxylizing. Then benzoic acid conjugated endogenous glycin and benzoyl glycocoll was produced. Monobutyl phthalate and benzyl phthalate conjugated endogenous beta-D-glucuronic acid and produced the glucurony-monobutyl phthalate and glucuronyl-benzyl phthalate.