1,4-Anhydroerythritol (1a) and 1,4-anhydro-L-threitol (1b) were polymerized using trifluoromethanesulfonic acid (CF3SO3H) or fluorosulfonic acid (FSO3H) as a cationic initiator. The polymerizations of la and 1b, proceeded through a ring-opening reaction with a proton-transfer reaction to produce hyperbranched carbohydrate polymers (2a and 2b) mainly consisting of erythritol and L-threitol units, respectively. The degrees of branching (DB) estimated by the C-13 NMR spectra of 2a and 2b were ca. 0.28-0.47. The weight-average molecular weight (M-w,(SLS)) values (3.2 X 10(4) - 5.1 x 10(5)) estimated using static laser light scattering (SLS) of the resulting hyperbranched carbohydrate polymers were significantly higher than the weight-average molecular weight (M,SEC) values (1.5 x 10(3)-1.4 x 10(4)) estimated using size exclusion chromatography (SEC). The solution viscosities of 2a and 2b were very low, and the intrinsic viscosities ([eta]) of 2a and 2b were in the range from 3.26 x 10(-2) to 7.30 x 10(-2) dL.g(-1). The three-dimensional properties characterized by the SLS and viscosity measurements indicated that 2a and 2b should be nanoscale particles.