Potato and sweet potato is an important food crop in the world. Crop consumption is gradually increasing, but production yields are declining due to injury of continuous cultivation or infection of soil-borne fungal pathogens such as Phytophthora infestans, Alternaria solani, Rhizoctonia solani and Fusarium spp. In order to find promising biocontrol agents, we have isolated 47 soil bacteria from potato cultivated soil and tested their antifungal activities. Among them, 3 strains were selected and identified as Bacillus velezensis RS15-1, B. velezensis RSS4-1, and B. velezensis PL1-1 using phylogenetic analysis based on 16S rRNA gene sequences. Subsequently we have optimized the medium formula using control of carbon, nitrogen mineral source for mass fermentation of B. velezensis RS15-1. In addition, in order to induce sporulation of the B. velezensis RS15-1, we adjusted temperature, pH and agitation speed in flask level. Initial incubation pH was measured from 6.83 to 7.81 and for OD600nm it was 4.8 for 39 hours. The final viable cell count by optimized conditions was measured at 2.37 × 109 CFU/mL.