A total of 448 Ross 308 seven-day old male broiler chicks were assigned to seven treatments with four replicates, each containing 16 chicks, to determine effects of physical sizes and rate of dietary inclusion of clinoptilolite. The chicks fed diet containing clinoptilolite at 1.5% and particle size of 0.4-0.8 mm showed significantly higher body weight gain than the control group that did not receive clinoptilolite (P<0.05). Adding clinoptilolite to the dietcaused a significant improvement infeed conversion ratio during 22-42 and 7-42 days of age(P<0.05). Broilers fed diet containing clinoptilolite at 1.5% and particle size of 0.4-0.8 mm had a lower feed conversion ratio than other groups. Addition of clinoptilolite at 1.5% and particle size of 0.4-0.8 mm improved protein efficiency ratio than the control group in periods 22-42 and 7-42 days (P<0.05). Broilers fed diet containing clinoptilolite at 3% and particle size of 0.4-0.8 mm had significantly longer villus height in the duodenumand those fed clinoptilolite at 1.5% and particle size of 0.4-0.8 mm had longer villus height in the jejunumthan the control group (P<0.05). Among different dietary treatments, the groupreceiving 1.5% clinoptilolite and particle size of 0.4-0.8 mm had thegreatest ratio of villus height to crypt depth. In conclusion supplementation of diet with clinoptilolite with a particle size of 0.4-0.8 mm had positive effects on performance and intestinal morphology in broilers. تفاصيل المقالة