The aim of this study was to determine the effects of Yucca schidigera extract added to lambs concentrate feeds containing urea on growth performance, carcass characteristics, some rumen and blood parameters. Forty-eight Merino male lambs were divided to one control and three treatment groups each consisting of three replicates of four lambs. Yucca schidigera extract was added to the concentrate feeds of control and treatment groups at the levels of 0, 200, 300 and 400 ppm, respectively. At the end of the study, rumen urea nitrogen levels of the lambs in treatment group 3 were higher (p<0.05) than those of control and treatment group 1. Blood urea nitrogen levels of the lambs in the treatment group 2 and 3 were lower (p<0.01) than those of the control and treatment group 1. There were no statistically differences in. warm and cold carcass weights, carcass yields and percentages of carcass meat, fat and bone of lambs in the control and treatment groups.