Abstract: The effect of dietary zeolite and initial weight on the performance and dressing percentage was investigated on Brown Swiss cattle. Forty cattle were weighed and sorted. Twenty heavier cattle weighing average of 207 kg were placed into 2 paddocks, 10 cattle in each paddock and 20 lighter cattle weighing average of 160 kg were placed into 2 paddocks, 10 cattle in each paddock. Treatments were; 1-one paddock of cattle in heavy group and one paddock of cattle in lighter group receiving 1% zeolite (ZE), 2-one paddock of cattle in heavy group and one paddock of cattle in lighter group not receiving zeolite (Control). When groups were pooled within treatments, ZE tended to have higher ADG and feed intakes than Control group. Control group tended to have higher dressing percentage than ZE group. Heavier cattle had higher daily dry matter intake and tended to have higher daily gain, lower feed efficiency and higher dressing percentage. Even though interaction between zeolite and initial weight was not significant, in terms of ADG and FE, receiving zeolite had greater effects on lighter cattle. It is concluded that using zeolite in feedlot diets increases performance and effect of different levels of zeolite should be investigated.