Bariatric surgery is considered the most effective treatment for reducing and maintaining weight for morbid obesity. Moreover, this surgery not only reduces weight but also improves comorbidity. However, concern about the safety of the surgery has grown with the favorable effects and has been heightened by high-profile reports in the death of a famous singer after bariatric surgery in Korea. In the beginning of the era of bariatric surgery, animal experiments had been conducted to improve surgical techniques in bariatric surgery. Among animals, a large animal such as pig and rabbit was used to develop and assess surgical skill. Recently, many researchers have been trying to investigate the mechanism of bariatric surgery for the resolution of morbid obesity and related comorbidities. An experimental model employing small animal has been developed to study underlying mechanism. We expect that this experiment will pave the way for developing a novel morbid obesity treatment.