The metabolic pathway for the degradation of cinnamic acid with Mucor sp. was studied by analyzing metabolites using GC-MS. β-phenethyl alcohol, for the first time, was detected as an intermediate in transforming cinnamic acid to acetophenone by Mucor sp. The metabolic pathway of cinnamic acid was supposed: epoxidation reaction was occurred on the double bond of cinnamic acid side chain to generate ethyl 2,3-epoxy-3-phenylpropionic acid, the epoxide was converted to β-phenethyl alcohol via decarboxylation and ring-opening reaction, lastly, acetophenone was produced from β-phenethyl alcohol via hydroxyl migration and oxidation reaction.