A novel graft polymer useful in various uses that has a polyolefin backbone having polyolefin segments excellent in moldability can be obtained by homopolymerizing a novel polyolefin macromonomer or polymerizing the novel polyolefin macromonomer in the coexistence of other olefins depending on need, wherein the macromonomer has at the terminal of its polyolefin chain a vinyl group whose .alpha.-position may be substituted, and the macromonomer can be efficiently obtained by a method, for example, successively carrying out i) a step of producing a polyolefin having a hydroxyl group at the terminal of the polyolefin chain and ii) a step of converting the terminal hydroxyl group of the polyolefin in chain into an acryloyl group, a methacryloyl group or a styryl group.