The putative raffinose synthase gene from rice was cloned and expressed in Escherichia coli. The enzyme displayed an optimum activity at 45 degrees C and pH 7.0, and a sulfhydryl group was required for its activity. The enzyme was specific for galactinol and p-nitrophenyl-alpha-D-galactoside as galactosyl donors, and sucrose, lactose, 4-beta-galactobiose, N-acetyl-D-lactosamine, trehalose and lacto-N-biose were recognized as galactosyl acceptors.