Abstract: No significant difference was found on hyphal growth rate of Rhizoctonia solani IA on PDA plates containing 0, 0.5, and 1.0 μg/mL Jinggangmycin A(J A). The virulent regression equation of the antibiotic is Y =3.2309+0.8720 X , r =0.9910,and EC 50 =106.9 μg/mL,EC 75 =634.5 μg/mL. Antibiosis experiments in vitro showed 74.1% inhibitory effect on PDA plate containing 50 μg/mL J A; under the conditions in vivo , a similar control effect (77.4% and 76.7%) was obtained by using only 50 μg/mL J A after 7 d and 14 d with J A treatment. By comparing the virulence of J A to R . solani AG 1 IA on cultural medium ( in vitro ) and on field rice plant ( in vivo ), we found that virulence of J A was 10 times in vivo more than in vitro . In the rice upper leaves treated with 1 μg/mL J A, activities of peroxidase (PO) and phenylalanine ammonia lyase (PAL) in the low sheath, which were involved in the biosynthesis of antimicrobial secondary metabolites, were also stimulated and the high enzyme activities were kept for more than two weeks under the greenhouse conditions. These results suggested first that not only there is the direct toxicity of J A against the pathogen but also defense reactions were triggered in rice plant upon the J A treatment.