In this study, we developed an implantable device for simultaneous optical observation and electrophysiological recording. The prototype image sensor was designed using a 0.35-μm standard complementary metal-oxide-semiconductor process, and green fluorescent protein fluorescence imaging of mouse brain slices was performed using the image sensor. In addition, a neural amplifier integrated on the same chip to amplify the weak neural signals obtained a midband gain of 39 dB at 40 mHz–3 kHz, and the input-referred noise was 4.9 μVrms. Crosstalk of the image sensor clock signal observed in the neural amplifier output was reduced using a software filter.