The efficacy of Mahonia bealei (Fort.) leaves extract (MBLE) against coccidiosis in chickens was studied in vivo. For this purpose, a total of 120 Hyland brown chickens (one-day-old) were randomly divided into six groups, each comprising 20 chickens, viz. MBLE-L, MBLE-M, and MBLE-H; drug control group; infected-untreated group; and uninfected-untreated group. Except for the uninfected/untreated group, the chickens in all other groups received an oral inoculation of 1.0 × 10⁴ pieces/feather sporulated oocysts of E. tenella on day 15. Then, for 7 days in a row, the drug control group was given sulfachloropyrazine sodium soluble powder (1.0 g/day) in drinking water, while the three treatment groups MBLE-L, MBLE-M and MBLE-H were given the MBLE @0.25, 0.5, and 1.0 g/day, respectively. The anticoccidial effects were evaluated by lesion score, body weight gain, oocyst output, and histopathological changes in the liver, kidney, and cecum of the chickens in each group. The results showed that no chickens died in all groups except 2 chickens died in the untreated group. The MBLE groups were able to decrease coccidia oocyst output, mitigate the impact of coccidian infection on chicken weight increase, and lessen pathological alterations in the liver, kidney, and cecum of infected chickens. Among these, the MBLE-H group demonstrated the greatest efficacy with an anticoccidial index of 159.17. Results showed that an extract from Mahonia bealei (Fort.) leaves extract had an anticoccidial effect on chickens infected with E. tenella.