Eighteen Rahmani lambs (initial body weight 30±1.3 kg and 5-6 months old) were used to determine the effect of different dietary fat sources on the performance, digestion coefficient of nutrients, ruminal parameters and carcass traits in a three months experiment. The animals were allotted into three groups, 6 animals per each. The animals of the first group were fed the control diet (without fat supplementation), while the animals of the second and third groups were fed diets containing 4% dried fat and 4% tallow, respectively. All experimental diets were formulated to provide the recommended levels of digestible energy    (3.0 Mcal/kg diet) and crude protein (14.71 %) according to NRC publication (1985) for sheep. There were a significant (P<0.05) differences in the average daily gain, daily feed intake (g/head/day), and feed conversion between the different experimental groups. Lambs fed ration contained 4% dried fat recorded the highest value in daily gain and the best feed conversion. The digestion coefficients of dry matter, crude protein, crude fibre and ether extract as well as the nutritive value (DCP and TDN) were significantly (P<0.05) higher for ration containing 4% dried fat followed by ration containing 4% tallow compared to the control one.Ruminal pH values were significantly higher (P<0.05) in lambs fed diet with 4% dried fat. Ruminal ammonia nitrogen and total volatile fatty acids concentrations were significantly (P<0.05) decreased with supplementation of fat compared to the control one.Dressing percentages were increased significantly (P<0.05) by feeding supplemental fat compared to the control group. It could be concluded that, lambs fed diet with 4% dried fat recorded the best performance and the highest digestibility and carcass traits.