This experiment was undertaken to investigate the effects of cation exchange capacity(C.E.C) and particle size of zeolite on the body weight gain, feed efficiency and nutrient utilizability when it was used in broiler rations at level of 3%. In this experiment, 9kinds of zeolite were used which have different level of C.E.C(80, 100, 120meq/100g) and different size of particle(20, 50, 90 mesh). The experiment was conducted from Oct. 21 to Dec. 16, 1977. with a total of 400 broer chicks. The results obtained are summarized as follows ; 1. Body weight gain was increased by supplement of zeolite(p$lt;0.05). Especially in the treatment of 120meq/100g in C.E.C and 50 mesh in particle size of zeolite, the body weight gain was superior to those of all other treatments(p$lt;0.05). 2. there was no significant difference in feed efficiency among treatments. However, slightly more feed was required per kg of body weight gain in all treatments constrained zeolite than in control. 3. The utilizabilities of dry matter, crude protein, crude fat and total carbohydrates of finisher diets were improved by addition of zeolite. Particularly in the crude protein utilizability, remarkable improvement was obtained. 4. Moisture content of poultry manure was slightly decreased by the supplement of zeolite at level of 3% in broiler ration. 5. Crude ash contents of zeolite supplemented feeds were higher than those of control diet and standard level of broiler ration officially fixed by ministry of Agriculture and Fishery.