This study was conducted to investigate the impact of age at the time of castration on the growth performance, carcass characteristics, and economic efficacy of Hanwoo (Korean native cattle) steers. This study included 344 calves with an average weight of 29.2 ± 4.5 kg, born between 2010 and 2016, at the Gangwon Livestock Technology Research Institute in Hoengseong, Korea. The 344 calves were divided into 4 groups based on age at castration: 6 months of age or younger (n = 47), 7–10 months of age (n = 74), 11–12 months of age (n = 96), and 13–15 months of age (n = 127). Body weight and length at 12 months of age increased with increasing age at castration (p < 0.05). Wither height, chest depth, chest width, chest girth, rump length, hip bone width, and rump width were lower in the group castrated at 6 months of age, compared with those in the groups castrated at older than 7 months of age (p < 0.05). Average daily gain (ADG) was higher in the group castrated at 11–12 months of age than in the groups castrated at younger than 10 months of age (p < 0.05). The carcass weight was higher in the group castrated at 11–12 months of age than in the groups castrated at younger than 10 months of age (p < 0.05). Marbling scores were higher in the groups castrated at younger than 10 months of age than in the groups castrated at older than 11 months of age (p < 0.05). Gross receipts and net income were obtained in the following order: castrated at 7–10 months of age > 11–12 months of age > younger than 6 months of age > 13–15 months of age. Body weight and body conformation traits at 6 months of age were positively correlated with age at castration, except for rump height (p < 0.01). Body weight and body conformation traits at 12 months of age were positively correlated with age at castration, except for rump height and pelvic width (p < 0.05). Live weight and carcass weight showed a positive (+) correlation with age at castration (p < 0.01), whereas marbling score and auction price showed a negative (-) correlation with age at castration (p < 0.01). The present results showed that castration at 7-10 months of age had positive effects on marbling and economic efficiency, while castration at 11-12 months of age had positive effects on growth performance and carcass weight. Thus, the suitable age for the castration of Hanwoo steers is 7–12 months.