This study was performed at the private Hanwoo farm, Hongcheon-gun in Kangwon-do with thirty two Hanwoo bulls and at the Samyang Taekwanryeong farm in Kangwon-do with forty Holstein bulls. They were assigned to completely randomized block design with alloting control and three doses of sustained release recombinant bovine somatotropin(SR-rBST), 0.03㎎/㎏ body weight (BWy14d(0.03mg group), 0.06㎎/㎏ BW/14d(0.06㎎ group) and 0.09㎎/㎏ BW/14d(0.09㎎ group). SR-rBST was administered biweekly and doses of SR-rBST were adjusted monthly according to BW increase. Initial average BWs of Hanwoo and Holstein bulls were 430㎏ and 334㎏, respectively. The purpose of experiment was to examine the effect of SR-rBST on growth and body conformation rate. The results are summarized as follows ; Average daily gains(ADG) of control, 0.03㎎, 0.06㎎ and 0.09㎎ groups were 1.02㎏, 1.18㎏, 1.11㎏ and 1.08㎏, respectively, for the experimental period in Hanwoo bulls. Administration of SR-rBST 0.03㎎/㎏ BW/14d, 0.06㎎/㎏ BW/14d and 0.09㎎/㎏ BW/14d moderately increased ADG by 15.7%, 8.1%o and 5.9%, to that of control group. Daily dry mater intakes were not different among treatments. These results indicate that SRrBST treatments tended to increase feed efficiency(FE). In ten items of body conformation measurements, SRrBST administration significantly increased withers height and chest width in comparison with control(P$lt;0.05) and 0.09㎎ group was more effective than other groups in Hanwoo. SR-rBSTs increased ADG in Hanwoo bulls by 4th month(average BW of 550㎏) after SR-rBST injection, however, ADGs at 5th and 6th month, at finishing period, were slightly decreased over control within monthes. In otherwise, ADGs of control, 0.03㎏, 0.06㎏ and 0.09㎏ groups in Holstein bulls were 1.20㎏, 1.28㎏, 1.16㎏ and 1.20㎏, and no statistical significances were found among treatments. However, ADG of 0.03㎏ group tended to be increased only 6.7%. SR-rBST treatments tended to increase body length, chest girth, chest width and ramp length in Holstein bulls. ADGs of 0.03㎏, 0.06㎏ and 0.09㎏ groups were decreased in comparison with control at lst and 2nd month after SR-rBST ingection, however, ADGs of those groups were increased at 3rd and 4th month(belong to fattening period) after SR-rBST injection. These results indicate that administration of 0.03㎎/㎏ BW/14d of SR-rBST increase meat productivity by increasing of ADG, FE and body conformation in fattening period.