A series of mononuclear Mn(II)/terpyridine complexes were synthesized and characterized by elemental analysis, IR spectrum, and UV-vis spectrum. Catalytic activities of Mn(II)/4 0 -Ar-2,2 0 :6 0 ,2 00 -terpyridine complexes were tested in the oxidation of cyclohexene or styrene in the presence of tert-butylhydroperoxide as oxidant. Significant catalytic effects of these complexes were observed in the oxidation of olefins, especially in the cyclo-oxidation of styrene.