Provided is a microporous film for a secondary battery, and more particularly, to a microporous film for a secondary battery with excellent quality stability and heat resistance, the microporous film comprising a 3 layer microporous film wherein: an inner layer that includes polypropylene of 20-80 wt % having a melting temperature of 150° C. or higher and a filler of 80-20 wt % having a melting temperature of 140° C. or higher, wherein a gross content of the filler and polypropylene in the inner layer is 60 wt % or more, and both surface layers which include polyethylene, wherein at least one layer of the both surface layers includes polyethylene of 70 wt % or more.