Introduction Microporous polyolefin separator is a key component of Ni-MH secondary battery because its basic properties were related with the performance and safety of the battery. Up to now, microporous polyolefins such as polypropylene separator were mainly applied. It is still require to be a strong mechanical spacing between positive and negative electrodes and have electronic resistace when submerged in the electrolyte. Also it should be minimum internal cell resistance and maximum cell space for electrodes etc. For this purpose, the application surface modification of conventional microporous polyolefin membranes are being continuously tried. The aim of the present study was to investigate effects of annealing temperature(45, 70 ?