Physical activity is powerful medicine that can change lives. An effective exercise prescription can improve strength, endurance, balance, function and quality of life. Physical activity epidemiological studies provide one of many types of research evidence that are necessary to assess the importance of physical activity to health. But, the assessment of physical activity level is very difficult and complex in elderly people. The major factors are culture, gender, age, disorders, motivation and cognitive function in elderly people for the assessment of physical activity level. There are two methods in order to assessment of physical activity level in elderly. Direct and indirect calorymetry, double labeled water, labeled bicarbonate and gas exchange. Indirect methods: The Ouestionnaire, heart rate, pedometer, accelerometer and physical activity index.