A microporous composite membrane comprising a microporous polyolefin membrane and a polypropylene-based coating layer formed on at least one surface of the microporous polyolefin membrane, the polypropylene having a mass-average molecular weight within a range of 5,000-500,000, and solubility of 0.5 g or more in 100 g of toluene at a temperature of 25.degree. C., and the microporous composite membrane having air permeability (converted to the value at 25-.mu.m thickness) of 50-10,000 seconds/100 cc.