A new meso-tetraalkyl porphyrin manganese complex, 5,10,15,20-tetrakis(ethoxycarbonyl)porphyrinatomanganese (Mn^IIITECPCl), had been prepared and characterized by X-ray structure determination. Mn^IIITECPCl exists as a coordinated dimer in its crystal structure with a weak antiferromagnetic coupling between two Mn(III) ions. The catalytic oxidation of styrene by Mn^IIITECPCl was carried out in acetonitrile. Mn^IIITECPCl was found to be recyclable with a high conversion efficiency when using TBHP as an oxidant and the major product was benzaldehyde. Mn^IIITECPCl was also reusable by using an PhIO oxidant, but the major products turned out to be phenyl acetaldehyde and styrene epoxide.