To provide a microporous polyolefin film surface-modified with a hydrophilic polymer, a surface modification method thereof, and a lithium ion polymer battery equipped with the microporous polyolefin film as a separator.

The microporous polyolefin film surface-modified with a hydrophilic polymer improves an electrolytic-solution impregnating ability by increasing the polarity and surface energy on the surface of a microporous polyethylene film and improves adhesiveness between the separator and an electrode, adhesiveness between the separator and an electrolytic solution, and adhesiveness between gel-like polymer electrolytes, by improving mechanical strength and heat resistance and by modifying the surface of the film to be hydrophilic, even though minimizing the deformation of the film by using a plasma coating method. Furthermore, the lithium ion polymer battery equipped with the microporous polyolefin film with the surface modified with a hydrophilic acrylic polymer as a separator is improved in its life and cycle characteristic.