To evaluate capacity of the elderly body and the extremities, we developed a measurement system for thigh cross-sectional image. The cross-sectional images were suitable for observing muscle volume. Some previous studies estimated muscular strength based on muscle volume measured the medical images. However there were no studies that used information regarding proportion in human extremities, e. g. muscles, subcutaneous fat and a bone. In this case, the measurements provide the same results even if the proportion is different among two people. We have investigated changes of thigh proportion by age and gender using the cross-sectional ultrasound images. In the survey, 150 ultrasound echo images and the body measurements (height, weight, and so on) were used. We conducted t-test between two groups that have different age, and discussed the causes of their differences. The statistical analysis revealed that the proportion of human thigh was dramatically changed with aging; the shape of thigh outline was deformed and the position of the thigh bone in the cross-sectional image was moved. We considered that the decreasing of the tissue elasticity with aging is responsible for these changes. The proportion analysis can be expected to be a new approach for developing a novel evaluation technique of the elderly body and extremity ability.