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The rate of the hydrogen chloride/methanol-catalyzed mutarotation of N-(p-chlorophenyl)-β-D-glucopyranosylamine has been studied polarimetrically at 16, 20, 25, and 30 °C. Rate constants and activation parameters have been determined for two parallel reactions. Enthalpies of formation, ΔHf^o, and entropies, S°, have been determined using the PM3 method for the various structures involved in the anomerization. The electrostatic potential around the p-chloroaniline N-D-glucoside molecule has also been calculated. The differences between the experimental and calculated activation parameters are discussed. A relatively stable acyclic immonium ion was found to be an intermediate of the reaction.