Twenty calves averaging 7Mo. of age were used to study the effect of zeranol implants(ZI) on growth, carcass traits and concentrations of hormone and serum metabolites in bulls and steers of Korean cattle. The animal were treated with none or three implants of zeranol at average ages of 7, 10 and 13Mo. There were significant(P$lt;0.05) differences between bulls and steers of control group in live weight, back fat thickness(BF), cold carcass weight and yield grade index. In steers, ZI increased serum IGF-1(Insulin-like growth factor-1) concentration, and resulted in greater live weight(10.5%) and BF(25.4%) compared to those of control. However, it did`nt affect marbling scores(P$gt;0.05). ZI in bullls tended to increase cortisol concentration, marbling scores and BF. The results indicate that zeranol implants had more advantage in steers than in bulls.