Unsymmetrical pyridinyl-imine complexes of cobalt (CoLn2, n = 1, 2... 6) containing functionalities attached to the alkyl or aromatic group bonded to the imino nitrogen were synthesized and evaluated as potential catalysts for epoxidation of styrene, and their related compounds were characterized by elemental analysis, 1H NMR, FT-IR, TG, et al. The influences of reaction conditions were further researched, including complexes, solvent, reaction tempreture, reaction time. The results showed that the complexes of cobalt(II) containing trimethylsiloxy attached to aromatic group bonded to the imino nitrogen (CoL42) was the most effective catalyst for epoxidation of styrene. These further explained that electron donating groups bonded to the imino nitrogen and the good steric effect of complexes increased the activity of the catalysts. Under optimal reaction conditions, the highest conversion of styrene was 99.9% with 62.4% styrene oxide selectivity.