Li dendrite formation has disturbed the usage of Li metal anode in rechargeable battery. Three dimensionally ordered macroporous polyimide (3DOM PI) separator is one of possible technology to suppress the dendrite formation. In order to optimize porous structure, an effect of pore size in 3DOM PI separator was investigated using three different pore size for separator (300 nm, 500 nm, 800 nm). An ionic conductivity of separator depended on size of pore. With decreasing pore size, the ionic conductivity of separator increased. Li Cu cell was employed to investigate an effect of pore size on morphology of lithium metal. 3DOM separator provided a uniform deposition of lithium metal and a suppression of dendrite formation. This is due to more uniform current distribution in 3DOM PI separator. The highest cycleability of lithium metal anode was realized by using smallest pore size 3DOM PI separator (300 nm). This is also related to uniform current distribution in the cell. (C) 2019 The Electrochemical Society.