The objectives of this study were to evaluate the effects of substituting barley with wet sugar beet pulp silage at differing levels on fattening performance, carcass quality and cost. To achieve this objective, a barley based diet (control diet) was prepared. Then, three diets were prepared by substituting 35% (35% WSBPS diet), 70 (70% WSBPS diet) and 100% of barley energy with wet pulp silage (100% WSBPS diet). A total of 48, 6-7 month old, male, Akkaraman lambs were utilized in the study. Lambs were randomly allotted into one of four groups based on initial body weights. Each group was also divided into 4 subgroups with 3 lambs within each subgroup and fed with one of four diets for a period of 75 days. Daily feed intake of each subgroup was determined weekly. All of the lambs were weighed bi-weekly to determine weight gains. Six lambs from each treatment group were slaughtered at the end of the experiment to determine carcass quality. Costs of each kg of diet DM and 1 kg of live weight gain for each diet were calculated. Initial live body weights of lambs fed different diets were similar, ranging from 23.48 to 25.03 kg (P>0.05). Overall daily weight gains of lambs fed different diet were also similar throughout the experiment and were 0.160, 0.182, 0.182, and 0.160 kg for control, 35%, 70% and 100% WPS diets, respectively (P>0.05). Hot and cold carcass weights, carcass tight, leg and loin weights were not statistically different among groups (P>0.05), but back weights were greater in sheep fed 75% WSP diet compared with control (P<0.05). Addition of WSBP silage into diets decreased both costs of diets and 1 kg live weight gain in a linear way. It can be concluded that energy provided by barley can be substituted with energy of WSP silage up to 70% without affecting fattening performance, carcass features and can greatly reduce production cost in lambs based on the results of the present study.