Magnetization-induced second-harmonic (SH) generation is studied in magnetophotonic crystals formed from a magnetic garnet spacer located between two dielectric Bragg reflectors, at the resonance of the fundamental radiation with the cavity mode. Longitudinal nonlinear magneto-optical Kerr effect manifests itself in the rotation of the polarization plane of a reflected SH wave which reaches a value up to 250°/μm. A magnetization-induced variation of the SH intensity is observed in transversal configuration with magnetic contrast up to 0.3.