This experiment was carried out to study the effects of monensin on the fattening performance and the efficacy of monensin against ovine coccidiosis. 18 male kids were randomly assigned to two groups of 9 head at monensin levels of 40 and 0 ppm. Two groups, of goats were fed ad libitum with the concentrate containing 1.3% CP and 70% TDN for 182 fattening days. The rice straw was used as the only roughage. The averages of initial and final body weight with monensin treatment and control were 13.0±2.0㎏, 12.4±2.0㎏ and 27.2±4.4㎏, 25.2±3.5㎏, respectively. The monensin treatment improved by 10% in both total body gain (14.2㎏ : 12.9㎏) and daily gain (78.1g : 70.8g), but the differences were statistically not significant. The feed conversions of monensin and the control were 7.5 and 8.3 respectively. The monensin improved feed conversion by 11%, but this difference was also statistically not significant Large numbers of coccidial oocysts in the feces of all kids were observed at the initial stage. From the 42nd day after monensin treatment, however, oocyst numbers began to decrease rapidly and from the 70th day oocyst were seldom found. but at the final stage of the fattening period (175∼182 days] oocyst numbers began to increase slightly