This study aims to analyze the effect of monensin antibiotic administration on weight gain and chicken performance. Broiler chicken is one of the poultry farms whose growth is fast, can meet the needs of meat in the community. To accelerate chicken growth, addition of Antibiotic Growth Promoter (AGP) was added to the beverage. The research method uses a Completely Randomized Design (CRD), consisting of 4 treatments and 6 replications. P0 Treatment (Control): Basal ration + Water boiled in 1 liter; P1: Basal ration + Boiled water + 0.1 gr / day Antibiotic Monensin in 1 liter of water; P2: Basal ration + Boiled water + 0.5 gr / day Antibiotic Monensin in 1 liter of water; P3: Basal ration + Boiled water + 1 gram / day Antibiotic Monensin in 1 liter of water. Data analysis used ANOVA one way variance and continued with the Least Significant Difference Test (LSD) with a confidence level of 5%. The results of the study by giving various concentrations of monensin antibiotics to broilers had significantly affected ration conversion, drinking water consumption and final weight. The administration of 1 gram monensin antibiotic concentration tends to be better for ration consumption, body weight gain, drinking water consumption and final weight of broiler chickens compared to lower concentrations or controls. Keywords: Broiler Chicken, Monensin, Performance