Cell suspension cultures of Lithospermum erythrorhizon, Gardenia jasminoides and Nicotiana tabacum were capable of glucosylating esculetin to esculin (7-hydroxycoumarin-6-O-β-D-glucoside). Especially, a culture strain of Lithospermum erythrorhizon was superior in the esculetin glucosylating capability; 40 to 50% of esculetin administered to the culture medium at early stationary growth stage was converted into esculin within 24 h. The rate of glucosylation was also dependent on the growth stage and the medium composition especially growth hormones and sugar.