PROBLEM TO BE SOLVED: To obtain a microporous film comprising a polyethylene with a raised liquid or gas permeability to the utmost while maintaining film thickness. SOLUTION: This microporous film has an excellent strength and fine particle preventing performances, good handleability and a remarkably improved liquid or gas permeability while maintaining a high porosity by regulating the structural factor to >;=1.5×;10<;7>; sec<;-2>; .m<;-1>; .Pa<;-2>; .