Catalytic epoxidation of olefins with molecular oxygen was studied in the presence of a sacrificial aldehyde using polynuclear manganese complexes of ligands, 2,5-dihydroxyterephthalaldehyde ([Mn-II(dhter)](n)) and its Schiff bases ([Mn-n(II)(Pdhteren)], [Mn-n(III)(Pdhteren)(OAc)(n)] and [Mn-n(III)(Pdhterpn)(OAc)(n)]) under different reaction conditions. Cyclohexene, cyclooctene, styrene, 1-hexene and 1-pentene were used as substrates for epoxidation. The influence of reaction medium, structure of aldehyde and nature of the ligand environment around catalytic metal center on epoxidation reaction was studied. The manganese(II)-Schiff base complex with nitrogen coordinating environment is more stable and effective epoxidation catalyst than the oxygen bound complex, [MnII(dhter)]. The catalytic system was used under heterogenized homogeneous condition using environmental friendly molecular oxygen as an oxidant. (C) 2002 Elsevier Science B.V All rights reserved.