TECHNOLOGY FOCUS - POLYMERS - Preferred Properties: The primary microporous layer has a standard deviation of normalized polypropylene/polyethylene ratio of 0.2 or less, kurtosis of normalized polypropylene/polyethylene ratio of -1 to 1, and average value of normalized polypropylene/polyethylene ratio of 0.5 or more, measured by Raman spectroscopy. The weight average molecular weight of polypropylene is more than 6x 104 and less than 3x 105. Preferred Composition: The content of polypropylene is 0.5 wt.% or more and less than 5 wt.% based on 100 wt.% total amount of polyolefin resin in the primary microporous layer. The multilayered microporous polyolefin film has a secondary microporous layer arranged between the surface layers. The secondary microporous layer contains polyethylene with terminal vinyl group concentration of 0.2 or more per 10000 carbon atoms measured by infrared spectroscopy. The multilayered microporous polyolefin film has a triple-layer structure in which secondary microporous layer is arranged between surface layers including primary microporous layer. The secondary microporous layer contains 20 wt.% or more polyethylene based on 100 wt.% total amount of polyolefin in the secondary microporous layer. The primary microporous layer contains polyolefin resin (p1) having terminal vinyl group concentration of less than 0.2 per 10000 carbon atoms. The polyolefin resin (p1) includes 45-99.5 wt.% high-density polyethylene having weight average molecular weight of 5x 104 or more and less than 5x 105, 0-50 wt.% ultrahigh-molecular weight polyethylene having weight average molecular weight of 1x 106 or more and less than 3x 106, and 0.5 wt.% or more and less than 5 wt.% polypropylene having weight average molecular weight of more than 6x 104 and less than 3x 105. The secondary microporous layer contains polyolefin resin (p2) having terminal vinyl group concentration of 0.2 or more per 10000 carbon atoms. The polyolefin resin (p2) includes 20-99 wt.% polyethylene having weight average molecular weight of 5x 104 or more and less than 1x 106, 0-79 wt.% high-density polyethylene having weight average molecular weight of 5x 104 or more and less than 1x 106, and 1-50 wt.% ultrahigh-molecular weight polyethylene having weight average molecular weight of 1x 106 or more and less than 3x 106, and does not contain polypropylene.