Sisay, A., Hassen, A. and Alemu, T. 1999. Effect of supplementation of molasses/urea blocks and graded levels of concentrate on growth performance of grazing Arsi bulls. J. Appl. Anim. Res., 16: 47–52. Thirty grazing Arsi bulls (24m, 130kg) were used in a 120 day trial to evaluate the effect of Molasses/urea block (MUB) with graded levels of concentrate supplementation on growth performance. These were divided into five groups and randomly allocated to five treatments in a completely randomized design. Animals on treatment 1 (T1) were grazed for 8 hours, whereas those in T2 T3, T4 and T5 were grazed for 8h and supplemented with ad lib MUB plus 0, 0.5, 1 and 2kg concentrate/head/day, respectively. Daily MUB and concentrate intakes and initial and final body weights were recorded. Growth rate of bulls were higher (P<0.05) in MUB supplemented than un-supplemented groups. Inclusion of concentrate with MUB further improved the growth rate of the bulls while MUB intake was reduced (P<0.05). Cost of supplement per unit of gain was lower (P<0.05) in T4 than in the rest of the treatment groups. It was concluded that MUB with 1kg concentrate supplementation is an economical and simple way of improving the growth performance of Arsi bulls grazing in the mid rift valley of Ethiopia.