The paper presents the research for the purpose of selecting microorganisms into the production process of "chao" to improve the quality of "chao" products and ensure food safety. Several analytical methods such as determination of formol nitrogen, determination of the protease hydrolysis activity, sensory evaluation method, experimental procedure, methods of analysis and processing of empirical data were used in this study. The findings showed that two out of four selected microorganism strains (one strain of fungi and three strains of bacteria denoted NM1, VK1, VK2, VK3, respectively) were the most appropriate for the cooperation among them and the production of "chao", which were coded NM1 and VK1. The suitable mixing proportion of strains of NM1 and VK1 was determined at 1:1.25, compatible with the 1:100 ratio of the varieties of microorganisms (in powder form) to tofu.