2,3-Anhydroerythritol (1a) and 2,3-anhydro-DL-threitol (1b) were polymerized using boron trifluoride diethyl etherate (BF3.OEt2) as a cationic initiator. The polymerizations of 1a and 1b proceeded through a ring-opening reaction with a proton-transfer reaction to produce hyperbranched carbohydrate polymers (2a and 2b) consisting of DL-threitol and erythritol units, respectively. The degrees of branching (DBs) estimated by the C-13 NMR spectra of 2a and 2b were 0.47 and 0.45, respectively. The weight-average molecular weight (M-w,M-SLS) values (2.67 x 10(5)-3.20 x 10(6)) estimated using static light scattering (SLS) of the resulting hyperbranched carbohydrate polymers were significantly higher than the weight-average molecular weight (M,,SEC) values (1.04 x 10(3)-2.77 x 10(3)) estimated using size exclusion chromatography (SEC). The viscosities of 2a and 2b in aqueous sodium nitrate (NaNO3) solution were very low, and the intrinsic viscosities ([eta]) of 2a and 2b were in the range from 0.0190 to 0.0250 dL g(-1). The three-dimensional properties characterized by the SLS and viscosity measurements indicated that 2a and 2b should be spherical molecules.