An object is to form a positive electrode active material having small and highly uniform particles by a simple process. A template is formed by forming holes in the template by a nanoimprinting method, and the template is filled with a gel-like LiFePO4 material, whereby small-sized LiFePO4 particles are formed and are used as the positive electrode active material of a secondary battery. The particle size can be reduced to less than 50 nm. Further, when the LiFePO4 particles are sintered, the template may be burned down. By making the particle size of the positive electrode active material smaller than the conventional one, a positive electrode that lithium is injected into and extracted from easily can be manufactured.