Provided is a porous film obtained by melt-kneading a high-molecular-weight polyolefin having a weight-average molecular weight of not less than 5 x 10 5 , a thermoplastic resin having a weight-average molecular weight of not more than 2 x 10 4 and fine particles, molding the kneaded matter into a sheet, and then stretching the sheet. The porous film can be easily and simply prepared, and has a high piercing strength, and hence can be advantageously used as a separator for a battery, particularly for a lithium secondary battery.