A U-bending test was designed by using a micro female mold with different groove widths and corner radii on a micro extension tester made by SANS company. The effects of the mold dimension and foil thickness on the maximum punch load, springback and surface quality were analyzed during the micro U-bending process. The results indicate that the reductions of groove width or radius leads to the increases of maximum punch load and the rates of increasing or decreasing of punch load increase greatly.By comparison of the punch loads of foils with different thicknesses,it is shown that the decreasing rate of punch load is larger than that of cross section area, and the size effect occurs obviously. Furthermore,the springback angle increases with the decreasing of thickness or radius, which reduces the accuracy of microparts. As the scratch appears at the side surface of a micro bending part, it suggests that the surface quality of the mold should be improved and the lubricating should be taken. The results have an important significance on the design of foil microforming process.