Ageratum conyzoides (Asteraceae) is folklorically used to treat diseases associated with bleeding. A study was conducted to determine the efficacy of Ageratum conyzoides in treating caecal coccidiosis of broilers. Acute toxicity test was done using thirty 28 days old broiler chicks which were divided into six groups of five birds each. The birds were given 250-3000 mg of extract/kg bodyweight orally. Group VI received equal volumes of distilled water. The birds were observed for 24h for signs of toxicity. Twenty-five growing broilers were divided into five groups of five birds each. At 35 days of age, birds in groups A to D were each infected orally with 8000 oocysts of Eimeria tenella. Fifteen days post-infection, groups A and B were treated with 500 and 1000 mg/kg of the extract, respectively. Group C received Amprolium in drinking water as 0.012 and 0.006% solutions for 7 days, respectively. Groups D and E were the negative and positive controls. No signs of toxicity were observed during the acute toxicity test. The faecal oocyst per gram of faeces decreased steadily in all the treatment groups until it became zero. The packed cell volumes, weight and red blood cell counts of the treated birds were significantly (P<0.05) higher than those of the infected untreated control. This confirms its ethnoveterinary use in the treatment of coccidiosis.