Abstract: Diclazuril, a new anticoccidial drug, was studied for its efficacy against chicken coccidiosis in battery trials and floor-pen trials. The high anticoccidial activity of diclazuril against Eimeria tenella was confirmed by the anlicoc-cidial index (195. 6) in two baitery trials. The floor-pen trials indicated that diclazuril at a dosage of 1 ppm in the feed was highly effective against mixed infections of three major pathogenic species E.tenella, E. acervulina and E.maxima in preventing mortality, suppressing cecal lesions and oocyst shedding, and allowing for normal weight gains as well as feed conversion.