Compositions for preventing plant disease injury which promote the formation of phytoalexin (i.e., an antibacterial substance sustained by plants per se) so as to enhance the resistance to disease injury inherent to the plants, little damage the environment and are inexpensive and highly safe. These compositions contain a mixture of at least one sulfur-containing amino acid selected from methionine, cysteine and cystine with D-glucose, These compositions are sprayed, either as such or after diluting 1 to 100,000-fold with water, onto the above-ground parts of plants. Alternatively, they are mixed directly with soil or soil is drenched with the compositions diluted 1 to 1,000,000-fold with water. <IMAGE>
