Abstract: Through liquid fermentation with M2 medium, the cell-free supernatant of Bacillus circulans FA13 strain, which isolated from deep-sea sediments of the South Atlantic Ocean, showed prominent inhibition activities against mycelial growth of Aspergillus parasiticus mutant strain NFRI-95 and aflatoxin producing. In order to maximize the yield of active substances, an uniform design was used to optimize fermentation conditions of the strain. After optimization, the inhibition efficacy of the 10-time diluted supernatant against Aspergillus parasiticus NFRI-95 mycelial growth and aflatoxin production was increased from 10.98% and 41.43% to 70.57% and 100.00%, respectively. The corresponding fermentation conditions were found as fermentation temperature 38.70 ℃, inoculum size 6.00%, volume fraction of seawater 0.00%, medium pH 8.71 and incubation time 6 days.