The transglucosylating reaction of the alpha-amylase (HGE) from Bacillus subtilis X-23 was studied using various phenolic compounds, catechins, and kojic acid as acceptors. Among them, hydroquinone, resorcinol, catechol, catechins, and kojic acid were glucosylated with high efficiency by HGE. In glucosylating kojic acid, kojic acid monoglucoside was accumulated at the end of the reaction. Analysis of the structure of kojic acid glucoside by H-1-NMR and C-13-NMR indicated that glucose was transferred to the hydroxymethyl group of kojic acid kojic acid and that the resultant compound was glucopyranosyl-alpha-O-2-methyl-5-hydroxy-gamma-pyrone. Comparing kojic acid and kojic acid glucoside, the solubility of the glucoside was about ten times that of aglucone. In addition, the stability of kojic acid was improved by glucosylation.