Three organocobalt compounds containing the vinyl group, viz. p-vinylbenzyl-Co(chel)B, chel = bis(dimethylglioxime), (DH) 2, bis(salicylaldehyde)ethylenediimine, SALEN, and bis(acetylacetonato)ethylenediimine, BAE, have been synthesized. Their radical polymerizations were studied using AIBN as initiator. They were not homopolymerized, but the latter two organocobalt monomers were copolymerized with styrene. The copolymerization rate constants increased with the half wave potential ( E 1 2 ) of the three monomers and polymerization did not occur at the presence of R · Co(DH) 2Py. E 1 2 of which had the minimum value among them. These findings suggest that the radical polymerization was inhibited by the redox reaction between the organocobalt compound and the radical. The reactivity ratios of p-vinylbenzyl · Co(SALEN)H 2O (M 1)-styrene(M 2) copolymerization were obtained ( r 1 = 0.77, r 2 = 0.25).