The crystal structure of form II of syndiotactic poly(l-butene) is presented. According to the present analysis, chains having a s(5/3)2 helical conformation are packed in a monoclinic unit cell with axes a = 15.45 Angstrom, b = 14.36 Angstrom, and c = 20 Angstrom and with gamma = 116 degrees The crystalline density is 0.933 g/cm(3) with four chains in the unit cell (40 monomeric units) : the space group is P2(1)/a.