This paper addresses on quality improvement of expanded food. The five stages of six sigma implementation process are applied to define the problem and set a target for improvement. Then possible causes to the quality problems in expanded food are investigated, and the capabilities of the measuring system are evaluated and improved. Based on the results, the experiment scheme is conducted to find and optimize the key factors. Improvement result shows that sigma level of production process increased to 4.6, which is beyond the expectation and can save the cost.