T-matrix approach is generalized to study the AC response of nonlinear metal/dielectric granular composites. We have derived general expressions for effective AC response at the fundamental frequency ω and the third harmonic 3ω and the fifth harmonic 5ω. When the components possess real dielectric response, our theoretical work reduces to the one with perturbative method. We take one step forward to perform numerical calculations on the metal/dielectric composites, and the results show that the effective third-order and fifth-order nonlinear susceptibility for fundamental and third-harmonic and fifth-harmonic frequencies can achieve large enhancement near the surface plasmon resonant frequency. Moreover, the resonant frequency exhibits a red-shift with increasing volume fraction of the nonlinear component. In addition, the effect of dimensionality on the effective nonlinear responses is studied.