To obtain a new raffinose synthase gene which hybridizes to DNA having a specific base sequence, codes for a protein having an ability of synthesizing raffinose from sucrose, and is useful to modulate an expression amount and activity of raffinose synthase in a plant.

This is a new raffinose synthase gene which hybridizes to DNA having a base sequence from 134 th to 2467 th shown by the formula under a stringent condition, consists of DNA which codes for a protein having an ability of synthesizing raffinose by making an α(1→6) bond at the hydroxy group which bonds to the carbon atom at position 6 of D-glucose residue in sucrose molecule, and can be used, for example, for techniques to modulate an expression amount and activity of raffinose synthase in a plant. This gene is obtained by amplifying/cloning cDNA, by the PCR using primers which consist of its partial sequence, which is synthesized from mRNA which is isolated from Brassica juncea by the conventional method.