For one-step enzymatic synthesis of eugenyl alpha-glucoside as a promising pro-drug for a hair restorer and a derivative of spices, selective alpha-glucosylation of eugenol was carried out using the alpha-glucosyl transfer enzyme of Xanthomonas campestris WU-9701. When 130 mumol eugenol and crude enzyme showing 1.0 unit of mu-glucosyl transfer activity were shaken in 2 ml of 10 mM H3BO3-NaOH-KCl buffer (pH 8.0) containing 1.2 M maltose as a glucosyl donor at 40degreesC, only one form of eugenyl glucoside was selectively obtained as a product and identified as eugenyl alpha-D-glu-copyranoside (alpha-EG) by C-13-NMR, H-1-NMR, and two-dimensional heteronuclear multiple-bond coherence analyses. In the reaction, no other glucosylated products such as maltotriose or eugenyl maltoside were detected in the reaction mixture. The reaction at 40degreesC for 48 h under the above conditions yielded 68 mumol alpha-EG in 2 ml suspension, and the maximum molar conversion yield based on the amount of eugenol supplied reached 52%.