The body fat measurements in old persons were carried out using two indirect methods; hydrostatic weighing and skinfold measurement.In comparison it was discovered that the skinfold measurement was significantly different from hydrostatic weighing method. Based on data of the circumference measurements which included forearm circumference (xl), arm circumference (x2), leg circumference(x3) thigh circumference(x4), abdomen circumference (x5) and buttock circumference(x6), two regression equations for the percentage of the body fat measurements were established as follows: male: F(%)=- 15.88 + 1.37BMI + 0.0102Y, female. F(%)= -34.9684 + 0.51BMI + 0.1469Y. Where Y = x1 + x2 + x3 + x4 + x5 + x6; BM1 (Body mass index) = weight(kg)/height(m)2Because the systematic error of skinfold measurements was bigger than those of circumference measurements, it was suggested that the above regression models could be used to estimate body fat in a simpler and easier way. At the same time the method of using percentage of body fat to classify obesity was compared with other two methods, excess body weight and BMI. The results showed that the rate of obesity based on BMI method was higher, and that based on excess body weight was lower than that of percentage of body fat measured by the water displacement method.