To determine the effect of physical activity on serum beta-carotene, we analyzed data about life styles including 3-day food records and blood samples collected from 57 men and 74 women in a rural city of Japan. Physical activity was asked as mean frequency of hard physical activities per week last year. A declining trend in serum beta-carotene was observed with increasing frequency of hard physical activities in men. In multiple regression analyses, the frequency of hard physical activities showed a negative partial correlation coefficient (r = -0.38, p = 0.007) with serum beta-carotene in men when controlled by age, BMI (body mass index), dietary factors (carotene intake, alcohol consumption and vitamin supplements use), smoking status, serum total cholesterol and serum triglycerides. These results suggest that frequent hard physical activity decreases serum beta-carotene especially in men.