In a previously study, the Bacillus sp. strain IA was successfully isolated with high sensitivity to rice husk biochar (RHB). Moreover, RHB promoted an antibiotic iturin A production by strain IA. In order to develop the biocontrol agent, we attempted to reveal the functions of the RHB in promoting the production of iturin A by strain IA. The promotion effects of growth, sporulation and iturin A production of strain IA by the RHB were explained as follows. First, the manganese ion, released from RHB, promoted the sporulation and iturin A production of strain IA. Second, the silicon dioxide contained in RHB adsorbed the metabolic inhibitor(s) and promoted the iturin A production of strain IA. Finally, the combination of manganese ion and silicon dioxide promoted the growth, sporulation and iturin A production of the Bacillus sp. strain IA. To culture strain IA in the medium combining manganese ion and silicon dioxide, the total cells, spore cells and iturin A production increased 15 times, 10,000 times and 18 times higher than the control medium, respectively.