This paper presents a multimodal neural activity monitoring system consisting of a double-high-pass-filter-based electrical-recording front-end and a fluorescence-recording front-end. The proposed electrical-recording circuit based on double high-pass filters is implemented by placing a narrow-band buffer in the feedback path of the low-noise and programmable-gain amplifiers so that low-frequency artifacts can be sufficiently suppressed during the electrical and fluorescence recording. The implemented system successfully measures the electrical signals and calcium ions in vivo for studying heterogeneous cell populations. For electrical recording, the front-end consumes the power of 2 uW/Channel and achieves the input-referred noise of 2.9 uVrms. The high-pass cutoff frequency can be programmed from sub-1 Hz to 300 Hz using the function of double high-pass filtering. For fluorescence recording, the front-end consumes the power of 10.8 uW/Block and occupies the area of 0.18 mm2/Block.