Micro-electro mechanical systems (MEMS) biochips realizing high-speed and high-efficiency of reaction and analysis attract much attention in medical as well as chemical fields. Especially, the miniaturized devices enabling small sample volume, arrayed, and portable measurement may become a powerful tool for material analysis and process control. We have proposed a novel micro optical diffusion sensor (MODS) which enables small sample volume, highspeed and non-contact measurement of diffusion coefficient of liquid sample. MODS consists of a pair of transparent electrodes (Al-doped Zinc oxide: AZO), a photoconductive layer (amorphous silicon: a-Si:H), two MEMS mirrors and excitation and probing fibers for inducing and detecting concentration distribution. The initial concentration distribution of sample is created by an opto-dielectrophoretic (opto-DEP) manipulation along with a sinusoidal pattern of irradiated beam on a photoconductive layer. In the present paper, the measurement principle is proposed, and the preliminary experiment using a bench top apparatus is reported.