Abstract: Activity of erythrocyte membrane ATPase and sialic acid content were measured in 42 young men （18—35 yearsold）, 30 middle-aged men （50—59 yearsold） and 39 elderlies（90—96 years old）. The results showed that membrane ATPase activity in elderly is markedly lower than that in the younger groups, and the membrane sialic acid content was also less in the elderly. This finding may suggest that the structure of red cell membrane undergoes some changes in the aging process, and that these changes may serve as indicators supervening of the physiological aging.