A multi-layer, microporous polyolefin membrane comprising a polypropylene
layer and a polyethylene resin layer and having well-balanced
permeability, mechanical strength, heat shrinkage resistance, shutdown
properties and meltdown properties can be obtained by (1) forming a sheet
comprising a gel-like polypropylene layer containing a membrane-forming
solvent or a polypropylene layer containing no membrane-forming solvent
and a gel-like polyethylene resin layer containing a membrane-forming
solvent, stretching the sheet at two-stage temperatures, and then
removing the membrane-forming solvent, or (2) forming a gel-like
polypropylene sheet containing a membrane-forming solvent or a
polypropylene sheet containing no membrane-forming solvent, and a
gel-like polyethylene resin sheet containing a membrane-forming solvent,
stretching them at two-stage temperatures, removing the membrane-forming
solvent, and then laminating the resultant microporous polypropylene
membrane and the resultant microporous polyethylene membrane.