The polymerization of beta-pinene with the AlCl3/SbCl3 binary catalyst was investigated in toluene at -40 degrees C and was compared with that of Lu-pinene. The polymerization of beta-pinene with AlCl3 alone was very rapid and retarded on addition of SbCl3, in sharp contrast to that of alpha-pinene where added SbCl3 remarkably accelerated it to give relatively high molecular weight oligomers. Attempted copolymerization of the two isomers with the binary catalyst, in turn, induced their parallel homopolymerizations, indicating that the copolymerization was difficult due to the large difference in reactivity. The homopolymerizations with AlCl3/SbCl3 were not seriously affected by a sterically hindered base, 2,6-di-tert-butyl-4-methylpyridine (DTBMP); the initiating species, therefore, would be different in nature from a proton.