A series of pyridylimine ligands with variations of the substituent at the imine nitrogen were synthesized and coordinated to the [MoCl 2 O 2 ] core. The novel molecular structures of the complexes were fully characterized by 1 H and 13 C NMR, FT-IR, ESI, EA, and X-ray crystallography, and their catalytic activity was studied for the epoxidation of alkenes using tert-butyl hydroperoxide (TBHP) as the oxidant. The new complexes showed excellent catalytic activity and fine selectiv-ity in the epoxidation reaction compared with similar homogeneous molybdenum complexes. The results demonstrated that there is a significant change in the catalytic performance, depending on the alkyl arm on the structure of the pyridilimine ligand. The catalytic results indicated that complex [MoCl 2 O 2 (L)] (L: N-(2-Pyridinylmethylene)-1-tert-butylimine) C 5 is the best catalytic precursor in the epoxidation of cyclohexene (TON: 92920 and TOF: 30974 h À 1).