Grazing cattle often require supplemental nutrients, especially at times when forages are dormant. To meet this requirement, producers have several options. They may supplement proteins or non-protein N (such as urea) or a combination. Urea is rapidly hydrolyzed to ammonia; consumption of high levels of urea could lead to ruminal ammonia accumulation, inefficient use of N by the animal and animal ammonia toxicity. Moreover, environment pollution is another problem when inefficient use of N occurs. Natural Zeolite is an Aluminosilicate with Cation Exchange and adsorption properties (Tomlinson, 1998). We hypothesized that Natural Zeolite can adsorb ammonia when its concentration in the rumen is high, and return it when ammonia concentration is low. Therefore, this effect can reduce ammonia toxicity and enhance calves performance and carcass traits. This study was conducted to determine the effect of natural zeolite on ammonia toxicity, carcass traits, performance and nutrient digestibility in finishing Holstein calves.