Abstract: A polyolefin synthetic pulp comprising a polyolefin resin graft-modified with an unsaturated carboxylic acid or a derivative thereof, and/or a polyolefin resin composition which comprises an ethylene/&agr;,&bgr;-unsaturated carboxylic acid copolymer and a polyethylene resin. Further, there is provided a heat sealing paper comprising a base fiber layer whose at least one surface is laminated and integrated with a layer of the polyolefin synthetic pulp. This polyolefin synthetic pulp has a large breaking length and an excellent internal bond strength, and exhibits stable heat sealing and hot tack properties over a wide temperature range from low to high temperature. The polyolefin synthetic pulp is suitable to use in battery separators, molding fiberboards, heat sealing papers and the like.