To explore the effect of orientation of monomers and polymerization procedure on polymerization behavior, thermal polymerization and photopolymerization of vinyl monomers having a biphenyl structure were conducted at various temperatures. It was found that the initial rate of polymerization and conversion increased with temperature despite phases of the monomer. It was also observed that Arrhenius plots for the initial rates of photopolymerization fell on a straight line, while those of thermal polymerization changed the slope at the smecticisotropic or nematic-isotropic phase transition temperature. The number-average molecular weight of the polymer produced in the thermal polymerization in the smectic phase was higher than that in the isotropic phase, whereas that of the polymer obtained by photopolymerization in the smectic phase was lower than that in the isotropic phase. These results suggest that polymerization behavior is affected by the initiation method in the polymerization of liquid-crystalline monomers.