The cyclopolymerizations of two meso dianhydrohexitols, 1,2:5,6-dianhydro-3,4-di-O-methylallitol (1) and -galactitol (3), were examined to form a polymer with six-membered ring repeating units. Distinct from the cases of 1,2:5,6-dianhydro-3,4-di-O-methyl-D-mannitol (5), -L-iditol (6), and -D-glucitol (7) in which the five-membered ring units were formed with high regio- and stereoselectivity, six-membered ring units were found in polymers 2b, 4a, and 4b obtained by the polymerizations of 1 and 3. The anionic polymerization of 1 with t-BuOK was highly regio- and stereoselective to form polymer 2a consisting of five-membered ring units, but that of 3 was different in the scission mode of the epoxy groups to form polymer 4a consisting essentially of six-membered ring units. The cationic polymerization of 1 with BF3. OEt2 produced polymer 2b having a structure consisting of the six-membered ring units as major constituents and five-membered ring units as minor ones. The structure of polymer 4b from the cationic polymerization of 3 was somewhat complex, comprising unknown units and uncyclized units along with the five- and six-membered ring units. The steric hindrance in the growing ion was an advantage in forming the six-membered ring unit.