In this paper we calculate the dynamic third-order nonlinear optical polarizabilities of three optical processes, third-harmonic generation, electric-field-induced second-harmonic generation, and degenerate four-wave mixing, for both ground and first excited singlet states in metal phthalocyanines in terms of the sum-over states formula. The transition moment elements and the transition energies in this formula are obtained using the INDO-SDCI method. The calculated second-order hypolarizabilities show a dispersion behavior with the difference from ground state and an enhancement of third-order nonlinear response in the first excited state. Among the PcM (M = H-2, Mg, Ni), there is a large enhancement of the first excited singlet state when there is a small third-order optical polarizability of the ground state. The calculated value of PcNi is compared with the observed one of the substituted PcNi in the order of magnitude. We also gain an understanding of enhancement mechanism for nonlinear processes in the excited state.