Abstract: This research was conducted in order to investigate the effects of supplemental fat and monensin on the level of Dry Matter Intake (DMI), Average Daily Gain (ADG), final weight, Feed Conversion Ratio (FCR), blood glucose level, Blood Urea Nitrogen (BUN), calcium, phosphor, triglyceride, cholesterol and crude protein of the Zel lambs; as well as commercial effects of monensin and supplemental fat on the lambs fattening. Most of the time, ordinary food does not suffice the animals needs. Thus, using high-energy materials like fats are important in programming the diets. Moreover, adding some materials to the animal diets could increase the animal efficiency and the products quality. Hormones, antibiotics, ionophores are amongst the most important additives affecting income in the lamb fattening industry. Monensin is the first ionophore component proven to be effective in increasing efficiency of ruminant animals. Twenty-four male Zel lambs were used with an age average of 3-4 months and an initial live weight of 21.94 ± 0.642 kg. A period of eleven days was considered as the adaptation time and the experiment was carried on during three 21-day phases (totally 63 days). The variables for this study were supplemental fat on two levels of 0 and 4% and monensin on tree levels of 0, 20 and 40 mg kg-1 on adrymatterbasis. There were four repetitions for each treatment. The results of this research reveal that different levels of fat and monensin do not have significant effect on DMI, ADG, FCR and level of glucose. The food treatment had significant effect on final weight, calcium level, BUN, phosphor, triglyceride, cholesterol and CP (p<0.05). Also, they affect commercial productivity.