The body mass index (BMI)is one of the important indexes to evaluate the nutrition / health status.BMI is weight in kilograms divided by height in per square meter (unit of kg/m2).BMI is changing with age.However,there are no BMI guidelines for the elderly.It is really necessary to set up a proper BMI range for the elderly.This research analyzed the relationship of BMI with all-cause mortality,cardiovascular mortality and body composition change in the elderly.The result showed that an appropriate higher BMI could help to decrease the all-cause mortality and cardiovascular mortality in the elderly and could also increase bone density and lean body mass,which could prevent the geriatric fracture and sarcopenia.Furthermore,underweight-related mortality was much higher than overweight-related mortality.