We report a MEMS-based tunable grating optical filter device and its integration with a fluorescence microscope system. This integration allows for voltage-controlled wavelength tuning of excitation light from a multi-band source. We demonstrate the system's capability to selectively excite fluorescence protein molecules with different excitation/emission spectral characteristics using a chip of optical filter device arrays, each with a very small (2mm x 2 mm) footprint. The demonstrated technology has potential to enable massively-parallel multispectral fluorescence microscopy in biochip array settings.