To provide a microporous film having excellent permeability and mechanical strength as well as excellent SD function at low temperatures and film-breaking resistance at high temperatures. A microporous film made of a resin composition at least comprising 1 to 50% by weight of a ring-opening polymer of an unsaturated condensed alicyclic compound, and 1 to 50% by weight of one or more resin components selected from the group consisting of polyolefins having a weight-average molecular weight of 500000 or less, thermoplastic elastomers and graft copolymers.