We proved the promotive effect of an Eucommia ulmoides OLIVER, leaf extract (ELE) on collagen synthesis by using collagen synthetic activity-reduced model rats (RMRs). RMRs were fed with a low protein diet and their collagen synthetic activity was assayed by the formalin-soaked filter paper pellet method When ELE was administrated to RMRs, the amount of collagen in granuloma was 1.6 times that of the control value. Thus, ELE stimulated collagen synthesis in RMRs. The administration of ELE might be useful for the prevention of aging.