This study was performed to determine the efficacy of feeding waste grapefruit silage vs. corn silage on performance and body composition of Kermani fattening lambs. Twenty seven male lambs weighing an average of 18.5±2.5 kg and again an average of 150±10 days old were randomly divided into three groups in a completely randomized design. For making waste grapefruit silage, the waste was chopped, mixed with wheat straw (4:1) and ensiled for 60 days. The experimental diets were: 1) corn silage 30% with 70% of concetrate (control), 2) 15% corn silage and 15% waste grapefruit silage with 70% of concetrate, and 3) 30% waste grapefruit silage together with 70% of concetrate. The lambs were fed TMR diets ad-libitum and twice a day. Daily dry matter intake, feed conversion, dry matter intake as percent of live weight, body weight, daily weight gain, and body fat percentage of fattening lambs were not affected by waste grapefruit silage. The feeding of waste grapefruit silage increased lambs’ bodies’ water content while decreasing the protein of the body (p<0.05). Feeding mixed corn and waste grapefruit silages the increased (p<0.05) the lambs’ body minerals. The results finally indicated that if there is waste grapefruit left over after human consumption, if can be enciled and fed to fattening lambs up to 30% of their diets.