| This study was conducted to investigate the effect of replacing mushroom cultivation spent (MCS) instead of barley in Awassi lambs ration on some carcass characteristics. Mushroom (Pleurotus ostreatus) spent were collected from Agriculture College, Tikrit's university mushroom farm, dried and mixed with rations. Thirty five local Awassi male lambs aged 5.5-6.5 months with initial weight of 30±0.39 kg were allocated to five treatments with seven lambs in each treatment and were distributed to

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... ndividual cages. The treatment groups were as follows: T1 (control treatment), T2 (5% MCS), T3 (10% MCS), T4 (15% MCS) and T5 (20% MCS). Percentage use of barley was minimized for each treatment ration in order to maintain a fixed percentage of protein (i.e., 14%). Wheat straw was provided ad libitum as a roughage diet while concentrate diet was provided @ 3% of live body weight for each treatment for the whole study period which was seventy days. After finishing the study period and before slaughter the lambs, slaughter weight was taken; thereafter other measurements were taken following the slaughter. Results showed significant decrease (p≤0.05) for T4 and/or T5 groups in each slaughter weight, empty body weight, hot and cold carcass weight, dressing percentage, fat tail percentage, backfat thickness, rib eye area and leg lean percentage, while there was no clear effect for MCS treatments on each forequarter and hindquarter cuttings, carcass and offal fat percentage. It can thus be concluded that it is possible to use mushroom cultivating spent (MCS) instead of barley in the ration of Awassi lambs within 15% without any negative effect on studied carcass characteristics.