The in vivo imaging is a one of the most important methods to uncover neural circuits. Many previous studies with confocal microscopes and fluorescence microscopes had been conducted. Those microscopes could get images which have high spatial resolution enough to detect cell bodies one by one. On the other hand, it has been difficult to observe circuits located deep in the brain below cortex. Recently, penetrable endoscopes using an optical fiber bundle or GRIN lens were reported to solve that problem. However, those optical recordings have very low temporal resolution compared to electrophysiological recording methods. We, therefore, developed a micro-endoscope system which enables us to record optical fluorescence and electrical neural activities simultaneously. The micro-endoscope was fabricated from a fiber bundle in which six-thousands of single mode fibers were bundled. The probe tip was gold-coated and further coated with enamel for insulation to be used as an electrode.Using our micro-endoscopic system, we could successfully in record fluorescence intensity change of calcium ion indicator dye, local field potentials (LFPs), and unit activities through endoscope tip at the same time from an identical recording site in the mouse's inferior colliculus (IC). In optical recording, calcium responses with sound stimuli were in the range of 3 ~ 6 %. There were several different activated areas activated by different sound stimuli in the same view field. In electrophysiological recording, neural activities were recorded at 20 kHz sampling. Thus, our micro-endoscopic system allows us to record calcium responses and electrical neural activities in the same area. By comparing calcium responses and electrical neural activities, we compensate for the temporal resolution problem of optical recordings. Thus, this new system will be useful in analyzing several neural circuits.