alpha-Arbutin, a useful cosmetic ingredient, was selectively synthesized by alpha-anomer-selective glucosylation of hydroquinone with maltose as a glucosyl donor using lyophilized cells of Xanthomonas campestris WU-9701 as a biocatalyst. When 45 mM hydroquinone and 120 mg of lyophilized cells showing 11 nkat of alpha-glucosyl transfer activity were shaken in 2 ml of 10 mM H3BO3-NaOH-KCl buffer (pH 7.5) containing 1.2 M maltose at 40degreesC, only one form of hydroquinone glucoside was selectively obtained as a product and identified as hydroquinone 1-O-alpha-D-glucopyranoside (alpha-arbutin) by C-13-NMR, H-1-NMR and two-dimensional HMBC analysis. Although hydroquinone has two phenolic -OH groups at the para position in its structure, only one -OH group, but not both -OHs, was glucosylated and no other glucosylated products such as maltotriose were detected in the reaction mixture. The reaction at 40degreesC for 36 h under optimum conditions yielded 42 mM alpha-arbutin, and the maximum molar conversion yield based on the amount of hydroquinone supplied reached 93%.