The aim of the research is focusing on the outcome of the decrease of defective rate during the period of producing ready-to-eat food with the method of five phases of Six Sigma, and to improve the quality step by step based on DMAIC. Through the data analysis in the past, critical-to-quality factor was identified and converted into the viable count in final product, and then the most significant factors affecting the viable count were selected by a variety of statistical analysis. In the meanwhile, design of experiments was implemented to find out optimal parameter of the factors and the effectiveness of the modification was confirmed. Finally, the final parameters were standardized and the relevant standard operating procedures were amended. The result shows that the problem of the viable count has been improved and the expenses on failure costs can effectively cut down.