The purpose of this study was to evaluate the maintenance of fitness with aging. The subjects were 59 men of 49-55 years of age, who entered to Hokkaido University and once had been examined for their fitness between the years of 1950-1952. They were reexamined to determine the maintenance of fitness with age in 1983. After 31-33 years, declination of the mean values in fitness shows from 50.9 to 42.1cm in vertical jump, from 154 to 143kg in back strength, from 4.35 to 3.73L in vital capacity and from 8.4 to 3.2 times in pull-ups. Grip strength was increased from 44.0 to 47.1kg. The correlation coefficients of the values between the time they were freshmen and the present time, were relatively higher in vertical jump (r=0.61, p<0.01), moderatory higher in back strength (r=0.50, p<0.01), grip strength (r=0.48, p<0.05) and vital capacity (r=0.46, p<0.05), but lower in pull-ups (r = 0.17, not significant). Back strenght and grip strength were maintained better in a group who had been engaged in daily physical activity than those who had been inactive. But the differences in the rate of decline were not significant in vertical jump; pull-ups and vital capacity. It was noticed that 14 (23.7%) of the 59 subjects indicated that walking was felt to be the most effective factor to maintain fitness.