Abstract: The kinetics of epoxidation of 1-octene with tert-butyl hydroperox-ide, in the presence of various molybdenum ( Ⅵ ) chelates, has been investigated,and the difference of catalytic properies of various Mo(Ⅵ) chelates been compared.The weaker the bond between Mo ( Ⅵ ) and its ligands in the chelate, the greater the rate constants for Mo(Ⅵ) chelate-catalysed epoxidation, but the stability of the Mo ( Ⅵ ) chelate is not adequate in the epoxidation system. On addition of excessive amount of donor to the system, the dissociation of Mo (Ⅵ) chelate is so much restricted that the Mo (Ⅵ) chelate loses its catalystic activity. However, in the presence of adequate amount of the donor, the Mo (Ⅵ) chelate can not only maintain its catalytic activity, but also increase its stability in the system.