We investigated the effect of glutathione supplementation on feed intake, body weight loss, behaviorchange and economic analysis of elk bull in breeding season. Sixteen elk bulls (5-year-old, average weight; 330kg) after antler cutting were divided into 2 groups. Eight bulls in each group (control and glutathione group)were fed experimental diet at a level of 0.85 percent of body weight and 6 mg glutathione per kg body weight.As a result, weight-loss of control animal during experimental study (from September to November) was42.6±19.2 kg while that of glutathione-supplemented group was 20.6±19.9 kg. Compared to control group,glutathione-fed group had prevented the body weight loss by 5.2% (p<0.05). Although the feed intake of elkvoluntarily decreases during breeding season, daily DM intake per head was 5.59 and 5.80kg in control andglutathione-fed group, respectively. While the statistical difference in feed intake between two groups was notobserved, feed intake tended to increase in glutathione-fed group. In economic analysis, additional cost of 99,000KRW per head was spent due to the cost of glutathione because of its import. Changes in behavior such ascrying, deer whistles, whistling intensity and frequency of accident were lower in glutathione-fed groupcompared to control. During breeding season, use of glutathione as feed supplement could suppress bodyweight loss and accidents in deer farm.