Abstract: Liquid cultures of antagonistic microorganisms(Bacillus sp．)were made．Changes of the activity of several enzymes in cucumber，watermelon，sweet pepper treated with the liquid culture were investigated also．The results show that compared with the activities of the control plants，those of the polyphenol oxidase，catalase，B-1，3-dextranase in the plant treated with the liquid cultures are on an obvious rise．Increasing rates of polyphenol oxidase activity in sweet pepper treated with 98-Ⅱ and in cucumber treated with 96-Ⅱ are 477．78％ and 150．O0％ respectively．Increasing rates of catalase activity in cucumber treated with 96-Ⅱ and 94-II are 419．64％ and 115．66％ respectively．Increasing rate of catalase activity in watermelon treated with 94-Ⅱ is 109．24％ ．Increasing rate of B-1，3-dextranase activity in cucumber treated with 98-I 23．90％ ．