This study was carried out to examine the anticoccidial effect of Citrus aurantium L ethanol leaf extract against the oocysts of Eimeria tenella isolated from broiler chickens. The fresh leaves of C. aurantium were collected from Emirate Garden, Katsina, authenticated, air-dried at room temperature, pulverised by milling and subjected to extraction. Sporulation inhibition bioassay was employed to examine the activity of C. aurantium ethanol extract on the sporulation of E. tenella oocysts. In this assay, deep well petri dishes containing 100 unsporulated oocysts were subjected to 2 ml of five different concentrations of the extract (2.5, 5, 10, 20 and 30 mg/ml) in triplicates while oocysts sporulated in 2.5% potassium dichromate solution (K2Cr2O7) and phenol served as control groups. The content of the Petri dishes was stirred to ensure adequate oxygenation. The experimental set-up was incubated at room temperature and examined after 24 and 48 hours for sporulation inhibition. The sporulated and unsporulated oocysts were determined by counting using the Mcmaster apparatus. Phytochemical screening of C. aurantium revealed the presence of alkaloids, saponins, carbohydrates, steroids and tannins. The result showed that ethanolic leaf extract of C. aurantium to possess anticoccidial activity against unsporulated oocysts of E. tenella in a concentration-dependent manner. There was significant difference (p < 0.05) in the sporulation inhibition activity, with the highest (97 ± 0.8%) at 30 mg/ml and the lowest activity (8 ± 1.0%) at 2.5 mg/ml concentration of the extract after 48 hours of incubation. There was a general trend of sporulation inhibition with an increase in the concentration of the plant extract. The findings from this study showed ethanol leaf extract of C. aurantium possesses a remarkable In vitro anticoccidial effect that may be further scientifically explicated.