The effects of dietary supplementation of urea-molasses multi nutrient block of lactating Horro cows fed Rhodes grass (chloris gayana) hay as a basal diet on milk yield, milk composition, feed intake and live weight change was studied on-station (at Horro Guduru Animal Production and Research Center of Wollega University). Sixteen cows in similar parity and lactation were randomly assigned to two groups: group A (control) and group B (UMMB-supplemented). The control group received baled Rhodes grass hay as a basal diet and small amount of concentrate; whereas the supplemented group (B) received UMMB in addition to the normal ration offered to the control group. The experiment was conducted for 60 days during the dry months. Mean daily milk yield and feed intake were higher in the cows supplemented with UMMB (P<0.01) compared to the un-supplemented group. The average milk yield for control and supplemented groups are 1.62 and 2.38 respectively. On the other hands no significant differences were observed among the supplemented and control group for milk composition and body weight gain (P>0.05). However the body weight gain is slightly better for the supplemented group. The increased milk production due to UMMB supplementation in this study could be attributed to the increased intakes of energy and nitrogen that was accessed through block supplementation.Keyword: UMMB Rhodes grass Milk yield Feed intake