Free volumes in thermotropic side-chain liquid-crystalline polymers were probed by positron annihilation technique. Lifetime spectra of positrons were measured in the temperature range between 130 and -60 degrees C in cooling. For a nematic liquid-crystalline polymer (polyacrylate), the lifetime of ortho-positronium (73) was decreased with decreasing temperature above the glass transition temperature (T-g, 21 degrees C) with larger temperature coefficient than that below T-g. The intensity of ortho-positronium (I-3) was constant above T-g. These facts mean that the size of the free-volume holes decreased with the decreasing the temperature but the concentration was almost constant in nematic phase. For a smectic liquid-crystalline polymer (poly(p-methylstyrene) derivative), a discontinuous decrease in the value of tau(3) and that of I-3 were observed at 107 degrees C, which was the transition temperature from smectic to crystalline phase. Such discontinuous changes were not observed for the polyacrylate specimen. This difference was considered to be attributed to the higher-ordered structure of the smectic phase.