Abstract: This study was carried out to determine the effects of diets containing 0, 75 and 150 ppm of Yucca schidigera extract (YSE) on fattening performance of Awassi lambs. Sixteen male Awassi lambs were allocated into three groups having similar live weight. The lambs in all groups were fed with a diet containing 134 g CP and 2756 kcal ME per kg dry matter during 63 days of fattening period. Results showed that supplementation of YSE in different dosage to the diet did not affect statistically live weight gain, feed intake and feed conversion ratio (p>0.05). However, total live weight gained at end of the fattening period slightly increased by feeding 150 ppm YSE and feed conversion ratio was improved compared to control group.