Using the extened Su-Schrieffer-Heeger model and the Sum-Over-State method, we have calculated the third-order nonlinear polarizability γ and its dispersion spectra for single substitutional fullerenes C77X(X=B or N atoms). The results indicate:(1) compared with C78,each of the static values of γ through the substitutional doping increases to some extent (3—40 times);(2) the dynamic nonliear optical reponse of C77X not only depends on doping atoms, but also depends on the substituted isomers and doped sites.