A microporous membrane according to the present invention is a microporous membrane containing a copolymerized high density polyethylene and a high density polyethylene, wherein a content of an α-olefin unit having 3 or more carbon atoms in the microporous membrane is 0.01 mol % or more and 0.6 mol % or less, and a viscosity average molecular weight of the microporous membrane is less than 300,000. In addition, a battery separator according to the present invention contains the above microporous membrane. Further, a battery according to the present invention contains the above battery separator.