Micro scale fluid control or mixing is critical for chemistry and life sciences. Successful performance of on-chip biochemical analysis processes, such as DNA hybridization and PCR amplification, highly depend on rapid mixing of multiple fluid species. In this paper, a set of initial designs is developed for flow mixing. In micro channels with 100 and 200μm width, alternating regions of hydrophobic/hydrophilic surface are created on silicon surfaces by photolithography and dry etch techniques. Experimental results show that in the micro channels with 20mm length, effective mixing is observed on the device patterned by incline hydrophobic/hydrophilic grilles in which eddy diffusion mixes two liquids. In contrasts, slight mixing is caused by the development of liquid instability induced by alternating hydrophobic/hydrophilic patterns orthogonal to the flow direction.