We investigated the body cooling capacity of water-circulated cooling pants during lower body exercise in a hot environment. Five subjects were asked to ride a bicycle ergometer and to keep a work rate of 75 W continuously for 20 minutes. They then rest on the ergometer for 15 minutes, in a climate chamber kept at WBGT = 31.5 degrees C. They repeated the same procedure three times under three different conditions; 1) wearing cooling pants with cold water supply; 2) wearing cooling pants without water supply; 3) wearing short pants instead of cooling pants. Esophageal temperature and heart rate of the subjects, when their cooling pants were supplied with cold water, were lower compared with the condition without water supply, and were almost the same as the condition wearing short pants. Water-circulated cooling pants should effectively cool the body at work where the worker has to wear pants that cover his legs to prevent injury.