We have measured the third-order optical nonlinearity of the organic-inorganic hybrid materials of supermolecules (C19H25N2)7Hn[P2Mo18-n VnO62] (n = 1, 2, 4, 5) and their reactants (C19H25N2)Br and Hn+6[P2Mo18-n Vn O62]by using the ultrafast optical Kerr effect at 830nm wavelength, with time resolution of 115fs. By comparing the γ values of the supermolecules and their reactants, it is concluded that the charge-transfer enhanced remarkably the third-order optical nonlinearity of the compounds. With the increment of the number of the vanadium atoms,the electron distribution changed strongly and the γ value decreased dramatically.