The cyclopolymerizations of 1,2:5,6-dianhydro-3,4-di-O-methyl-D-mannitol (1) and -L-iditol (2) were carried out using BF3 . OEt(2) and SnCl4. The polymers obtained were soluble in chloroform, methanol, tetrahydrofuran, and water but insoluble in n-hexane. The specific rotations ([alpha](22)(546)) of the polymers were +41.3 to +73.2 degrees for 1 and +38.2 to +62.9 degrees for 2 (c = 1.0, CHCl3). For all the polymers, the extent of cyclization was 100%. The structure of the polymers obtained from both 1 and 2 was (1-->6)-bonded 2,5-anhydro-3,4-di-O-methyl-D-mannitol as the 5-membered constitutional unit, namely, poly[(1-->6)-2,5-anhydro-3 ,4-di-O-methyl-D-glucitol]. The n-hexane-soluble products, which were obtained together with the n-hexane-insoluble polymers for the polymerization using BF3 . OEt(2), contained 1,6:2,5-dianhydro-3 ,4-di-O-methyl-D-glucitol, the cyclic dimer of 2,5-anhydro-3,4-di-O-methyl-D-glucitol and its higher cyclic homologs.