Raffinose is produced by allowing a raffinose synthase having the following properties to act on sucrose and galactinol: (1) action and substrate specificity: produces raffinose from sucrose and galactinol; (2) optimum pH: about 6 to 8; (3) optimum temperature: about 35 to 40.degree. C.; (4) molecular weight: (i) about 75 kDa to 95 kDa estimated by gel filtration chromatography; (ii) about 90 kDa to 100 kDa estimated by polyacrylamide gel electrophoresis (Native PAGE); and (iii) about 90 kDa to 100 kDa estimated by SDS-polyacrylamide gel electrophoresis under a reduced condition (SDS-PAGE); and (5) inhibition: inhibited by iodoacetamide, N-ethylmaleimide, and myo-inositol.