In this study, we examined surface plasmon resonance (SPR) induced magneto-optical (MO) Kerr signals, and obtained a complete SPR curve in multilayered metallic structures comprising 6-nm-thick Au, t-nm-thick Permalloy (Py), and 26-nm-thick Au layers (with various thicknesses of Py). As the thickness of the Py layer increased, the SPR weakened. The MO signals were exhibited to various magnitudes of amplification while measuring the hysteresis loop at different segments of the SPR curve, which were the product of the MO Kerr effect. The MO signals between the reflectance maximum and reflectance minimum of the SPR were enhanced significantly in the samples with a 2 to 20-nm-thick Py layer. After measuring and analyzing the MO signals from multiple specimens with various thicknesses of Py, the optimal thickness of the Py layer was 10nm, at which the strongest signal amplification was obtained.