Objectives: This study was designed to evaluate the ability to inhibit the cytotoxicity associated with oxidative stress in MCF-7 and Hep-G2 cells of B subtislis KP3 extracellular secretions and intracellular extractions. Methods: The cytotoxicity of extracellular secretions, intracellular extraction of B subtilis KP3 and stress-induced agents' hydrogen peroxide upon Hep-G2 and MCF-7 was determined by MTT test.