Magnetoplasmonic sensors are attractive candidates for ultrasensitive chemical and biomedical sensor applications. A variety of ferromagnetic metal thin films have been used for magnetoplasmonic device applications, yet the dependence of sensor performance on the optical and magneto-optical properties of ferromagnetic metal materials has been rarely studied. In this work, we report the study of enhanced magneto-optical Kerr effect (MOKE) and sensing performance in Au/FexCo1?x bilayer magneto-optical surface plasmon resonance (MOSPR) transducers. The optical constants of FexCo1?x (x=0, 0.29, 0.47, 0.65, and 1) in a sputter-deposited Au/FexCo1?x device are characterized by the attenuated total internal reflection (ATR) method. FexCo1?x thin films show different MOKEs as a function of the chemical concentration, with the highest transverse MOKE signal observed in Fe0.7Co0.3. Index sensing performance is closely related to the material’s optical and magneto-optical constants. By studying the sensing performance in the parameter space of the Au/FexCo1?x bilayer thicknesses, the highest sensitivity is found to be 0.385 (theoretical) and 0.306 RIU?1 (experimental) in the Au/Fe0.7Co0.3 MOSPR devices. Our research highlights the influence of the optical properties of ferromagnetic material to device sensitivity in MOSPR transducers. The high sensitivity in Au/FexCo1?x MOSPR devices make these structures attractive candidates for chemical and biomedical sensing applications.