The crystal structure of the clathrate form of syndiotactic poly(p-methylstyrene) (s-PPMS) containing o-dichlorobenzene (o-DCB) is presented. The structure is characterized by polymer chains in s(2/1)2 helical conformation and o-dichlorobenzene molecules packed in a monoclinic unit cell with axes a = 23.4 Angstrom, b = 11.8 Angstrom, c = 7.7 Angstrom, and gamma = 115 degrees, according to the space group P2(1)/alpha. The calculated crystalline density is 1.07 g/cm(3) for two polymer chains (eight monomer units) and two o-DCB molecules included in the unit cell. The o-DCB molecules occupy cavities delimited by the phenyl rings of two enantiomorphic polymer chains. A disorder in the positioning of the o-DCB molecules inside the cavity is present. A comparison with the crystal structure of the clathrate form of s-PPMS containing tetrahydrofuran is presented. Remarkable differences were found, confirming the previous hypothesis that two different types of crystal structures (alpha and beta class) are presented by the clathrate forms of s-PPMS depending on the guest molecule.