Polymer-immobilized cobalt-EDTA complex was prepared by grafted copolymerization of methacrylic acid (MAA) and acrylonitrile (AN initiated by redox initiation of EDTA-2Na (Ethylenediamine tetraacetic acid disodium salt) with ceric ion (Ce2+)). High yield and selectivity for peroxidation of benzaldehyde were obtained when using the polymer-immobilized cobalt-EDTA complex as a catalyst. With the concentration of benzaldehyde increasing, the concentration of perbenzoic acid was increased from 0.38M to 0.98M, but yield of perbenzoic acid decreased from 0.76M to 0.65M. With the amount of the polymer support increased, the yield of perbenzoic acid increased from 70% to 82%. The selectivity remained about 82% in the various amounts of the polymer support. The activation energy of peroxidation of benzaldehyde was 43.4 KJ/mole. The expression of the reaction rate was: r(i) = k [RCHO](o)(1.0) [polymer support](0.5). A mechanism for peroxidation of benzaldhyde catalysed by polymer-immobilized cobalt-EDTA complex was proposed in this investigation.