Novel catalysts for the hydroxylation of phenol, Fe-Si-O, Fe-Mg-O and Fe-Mg-Si-O complex oxides, have been synthesized by a coprecipitation method. X-ray diffraction studies show that MgFe2O4 crystallites with spinel structure are formed in Fe-Mg-Si-O and Fe-Mg-O complex oxides and the crystallite size of the metal oxide or complex oxide is reduced after addition of Si. In the hydroxylation of phenol with hydrogen peroxide, Fe-based complex oxides exhibit high activities after a short induction period. The phenol conversion is improved when silicon is introduced into the Fe-based complex oxides, and formation of MgFe2O4 crystals with spinel structure in the catalysts increases the diphenol selectivity. The addition of a little acetic acid to the reaction liquid can shorten the induction period effectively. Under the same reaction conditions, phenol conversion and diphenol selectivity over the Fe-Mg-Si-O catalyst are close to those over TS-1, and furthermore, the reaction time is more than ten times shorter as compared to TS-1. The reaction mechanism of the hydroxylation of phenol on the catalysts has been studied, and a free-radical mechanism initiated by the formation of phenoxy free radicals is suggested.