A strain of bacterium a45, an antagonist to capsicum wilt ( Ralstonia solanacearum ), was isolated from the rhizosphere of capsicum. The strain was identified as B. subtilis according to its physiological and biochemical characteristics and 16S rDNA gene sequence. 20%（V/W）of a45 culture was inoculated into a mixture of pig manure compost and amino acid fertilizer, which fermented for 4 days into bio-organic fertilizer (BOF) containing about 2.0×10⁹g^-1 soil of a45. A pot experiment was carried out in greenhouse using soil inoculated with pathogen Ralstonia solanacearum(9.6×10⁶g^-1 soil), and amended with either BOF (5‰ W/W，1.0×10⁷ a45 g^-1 soil) or a45 liquid culture (LC,1.0×10⁷ a45 g^-1 soil) to evaluate effect of the bio-control agents in controlling the wilt disease. Results show that the application of LC and BOF mitigated capsicum wilt incidence by 69.58% and 76.09%, respectively, and promoted growth of the plants somewhat. The population of Ralstonia solanacearum in the capsicum rhizosphere 30 days after application with LC and BOF was decreased by 20.5% and 25%, respectively compared with that in the control. And the population of a45 decreased gradually over time after inoculation in both soils. However, BOF significantly deferred the decrease as compared with LC. Besides, genes ituA、ituB、ituC、ituD，Qk，bam and SboA responsible for synthesis of antibiotics iturin, subtilisin QK, bacillomycin andsubtilosin A, respectively, were detected in strain a45 with PCR, showing that the strain can be used as a biocontrol agent.