Bacillus cereus BS229 was identified as a bacteriocin producer with a bactericidal activity against Bacillus thuringiensis subsp. Thomsoni BR-40. Bacillus cereus BS229 and cerein BS229, named tentatively as the bacteriocin produced by Bacillus cereus BS229, showed a narrow spectrum of actibity against Gram-positive and Gram-negative bacteria, along with yeast and molds. Production of cerein BS229 in a 5-1 fermenter followed typical kinetics of primary metabolite synthesis. The antibacterial activity of cerein BS229 on sensitive indicator cells disappeared completely by ${alpha}-chmotrypsin$ or proteinase K, which indicates its proteinaceous nature. Cerein BS229 seemed to be very stable throughout the pH range of 2.0 of 9.0 and it was relatively heat labile, despite the fact that bacteriocin activity was still detected after being boied for 30min. Cerein BS229 actibity has been changed with some of the organic solvents such as toluene, ethanol, and chloroform. Direct detection of cerein BS229 actibity on SDS-PAGE suggested that it had an apparent molecular mass of about 8.2 kDa.