In recent years, coccidiosis has been still a problem both in concentrated poultry husbandry as well as free-range husbandry in provinces in the country. The study was implemented on the breeding poultry heard Ross-308 at the company in Pho Yen showed that: 21.28 percent of the surveyed total of Ross-308 chickens was infected with cocci. Slightly infected chickens were mainly and occupied about 51.08 percent and very severely infected chicken occupied just about 2.89 percent. Th~ infected rate and frequency varied according to ages, especially chicken at the ages of over 2-5 weeks of age with the highest infected rate 31,88 percent and severely infected frequency was 5.88 percent. Coccidiosis of Ross308 chickens displayed in both seasons, the autumn and the winter, it, however, was higher in the autumn than that in the winter, 25.] 9 percent and ] 9.72 percent respectively. The result of operation to determine coccidiosis of the Ross-308 breed showed a greatest level, 70.38 percent in caecum and 14.76 percent in rectum. Both Hanzuril-25 and Anti coccidae-diarrhoea did not negatively affect on chicken's survival rate.