Impact of intestinal microbes on obesity and health is a new topic recently started to get attention. Comparing to the global concern and research trends, there are few research on the association between intestinal bacteria and life style disease in Korean. One voluntary case (female) was reported to show the change in gut microbiota and weight by diet intervention. She was overweight (BMI 23.2 kg/m²) and has abnormal liver function, and the causes of overweight were frequent drinking and meat consumption at the late evening hours. For 47 days, she was administered an improved diet on breakfast and dinner with reduction of meat consumption frequency by 50%. Alcohol consumption was reduced to once a week. As a result, she lost 3 kilograms of body weight. Her fecal sample was collected before and after the intervention, and gut microbiota change was compared using a high-throughput sequencing technique. After diet correction, the shift of gut microbiota was clearly observed with decreased proportion of Firmicutes (from 75.7% to 47.3% in total microbiota) but increased proportion of Bacteroidetes upto 47.7%. After incorporating the diet intervention, it is meaningful to confirm the changes in dominant gut microbiota and weight loss.