We have developed a novel micro optical diffusion sensor (MODS) based on a laser induced dielectrophoresis (LIDEP) enabling small sample volume, high-speed measurement and on-site sensing of the protein conformation. This paper reports the measurement principle, chip design, and the validity of the proposed method. In order to verify the applicability of MODS, we confirmed the sinusoidal concentration distribution of polystyrene beads in distilled water generated by LIDEP force. The decay time of the diffusion of the concentration distribution agreed well with the theoretical calculation. As a result, the applicability of MODS as the diffusion coefficient measurement method was verified.