Enhancement of the longitudinal Kerr effect by excitation of surface plasmon resonance (SPR) in ferromagnetic Co72Fe8B20/Au stacked films was investigated in a Kretschmann configuration with p-polarized light at 633 nm. We found that (1) it was possible to excite SPR in the bi-layer structure of Co72Fe8B20/Au with the necessity of the Au layer faced to air. We also found that (2) the dependence of the longitudinal Kerr effect on the incident angle indicated that the saturation component of ellipticity was bell-shaped in the hysteresis loop, while the rotation angle had a dispersed-shaped distribution. In contrast, the rotation angle was bell-shaped for the linear component, while the ellipticity had a dispersed-shaped distribution. Moreover, we discovered that (3) the saturation component of the longitudinal Kerr effect in the Co72Fe8B20/Au (20 nm) stacked film had a steep maximum as a function of the thickness of the ferromagnetic layer, and that the strongest resonance occurred at a ferromagnetic layer thickness of 8 nm. In addition, we found that (4) the linear component of the longitudinal Kerr effect was caused by the Faraday effect of the prism and glass substrate, which was extremely enhanced by SPR.