Solid state structure has been studied for a series of recently synthesized liquid crystalline polycarbonates(1) based on methyl-substituted stilbene mesogen and methylene-containing flexible spacer. These polymers are referred to as HMS-n, where n is the number of methylenes in the flexible spacer group. The stability of the liquid crystalline phase and its relationship to the three dimensional crystalline phase were studied. X-ray diffraction patterns of raw fibers drawn from the mesophase revealed that the stability of the mesophase decreases as the methylene spacer length gets close to that of mesogen. From X-ray diffraction patterns of annealed fibers and molecular modeling studies, the unit cell parameters of HMS-5 to 8 were determined. HMS-5 and 6 have an orthorhombic structure while HMS-7 and 8 have a monoclinic structure. More important, an odd-even oscillation is observed in the d-spacings of the (0 2 0) and (1 1 0) reflections as a function of n, which relates to differences in interchain packing in the odd and even members of the series. All HMS-5 to 8 have a stable intermeshed crystal structure in which the mesogen and the flexible spacer group on adjacent chains are aligned. In this structure the disposition of the carbonate group differs from n-even to n-odd, and is responsible for the odd-even effect seen in the two dominant interchain d-spacings. We suggest the higher degree of overlap of the carbonate linkage of HMS-7 and 8 might be the reason for their less stable mesophase compared with HMS-5 and 6.