This experiment was conducted to investigate if usnic acid, a lichen metabolite, exerts therapeutic action against coccidiosis. A total of 160 one-day-old male Ross 308 broiler chicks were divided into 5 experimental groups (A-E), each replicated in 4 pens of 8 chicks. At 16 days of age Groups B-E were infected orally with a mixture of purified oocysts including 30 x 10(4) sporulated oocysts from field isolates of E. acervulina, E. brunetti, E. maxima, E. mitis, E. praecox and E. tenella, whereas Group A was remained uninfected. Seven days after the coccidiosis induction, infected birds were divided into 4 groups to receive orally with 20 mg usnic acid (Group C), 100 mg usnic acid (Group D) and 7 mg toltrazuril (Group E) per kg body weight. The birds in Group B were untreated and served as infected control. The experiment was terminated at 29 days of age. As a result of the study it was evaluated that infected birds had lower feed intake and body weight and worse feed conversion, higher intestinal lesion score, longer small intestine and cecum, and higher fecal oocyst count than healthy birds. The anticoccidial effect of usnic acid at 100 mg/kg application dose was comparable to toltrazuril as reflected by alleviations in performance and pathology findings. In conclusion, it is demonstrated that usnic acid possesses some anticoccidial effects, but not nearly as good as toltrazuril.