A miniature process for separating the oil phase from dilute oil/water emulsion is developed. This process applies a confined space apparatus, which is a thin flow channel made of two parallel plastic plates. The space between the two plates is rather narrow to improve the collisions between oil droplets and the plate surface. Oil droplets have an affinity for the plate surface and thus are captured, and then coalesce onto the surface. The droplet size distribution of the residual emulsion resulted from the separation process is remarkably changed. The oil layer on the plate weakens the further separation of oil droplets from the emulsion. Three types of plate materials, polypropylene (PP), polytetrafluoroethylene (PTFE) and nylon 66, were used. It is found that PP is the best in terms of the oil separation efficiency and nylon 66 is the poorest. The interaction between droplets in the emulsion and plate surface is indicated by the spreading coefficient of oil droplet on the plate in aqueous environment, and the influences of formed oil layer and plate material on the separation efficiency are discussed.