The crystal structue of a highly isotactic optically active alternating styrene-carbon monoxide copolymer, obtained with a chiral cationic Pd(II) bioxazoline complex, is determined and refined from powder X-ray diffraction data with the Rietveld method. The unit cell is monoclinic, P2(1) space group, with a = 8.367 Angstrom, b = 7.574 Angstrom (chain repeat), c = 5.47 Angstrom, beta = 110.0 degrees, and Z = 2 monomeric unis with a density of 1.32 g/cm(3); The observed chain conformation has a repeat period almost identical to that observed in syndiotactic copolymers in spite of the different symmetry connecting the monomeric units, s(2/1) instead of tc. The different symmetry connecting the monomeric units along the chain influences significantly the reciprocal orientation of the phenyl groups within each chain and between different chains.