Cyclopolymerization of unsymmetric and symmetric Si-containing alpha,omega-diolefins by dimethylpyridylamidohafnium/organoboron catalytic system with high cyclization selectivity and stereoselectivity was first reported here. Compared with the constrained geometry catalyst [Me2Si(eta(5)-Me4C5)((NBu)-Bu-t)]TiCl2 and the typical metallocene catalyst rac-Et(Ind)(2)ZrCl2, the Hf complex has proved to be one more promising catalyst for the cyclopolymerization of unsymmetric 3,3-dimethyl-3-sila-1,5-hexadiene (DMSHD). The poly(DMSHD) with high molecular weight (up to 953 kg/mol), high cyclization selectivity (100%), high cis selectivity (>90%), and high isotactic selectivity (>90%) could be easily obtained by the catalyst under mild conditions. Moreover, the poly(DMSHD) also possessed a high glass transition temperature (up to 99.8 degrees C) and high melting temperature (T-m >200 degrees C). The insertion reaction of the vinyl group into Hf-C-Ar bond was further investigated, and a possible cyclization mechanism of DMSHD was proposed according to density functional theory calculation. Meanwhile, the Hf catalyst also showed notable catalytic activity for the cyclopolymerization of the symmetric Si-containing alpha,omega-diolefins including 4,4-dimethyl-4-sila-1,6-heptadiene, 4-methyl-4-phenyl-4-sila-1,6-heptadiene and 4,4-diphenyl-4-sila-1,6-heptadiene. Although the cyclization selectivity is somewhat low, the copolymerization by Hf catalyst still shows excellent cis/trans selectivity and isotactic selectivity.