ix This experiment was conducted to evaluate different levels of effective microorganism treated teff straw supplementation with concentrate feed on nutrient utilization and performance of yearling intact local lambs at Sirinka Agricultural Research Center. The experiment was conducted using 25 yearling intact local male lambs with an average initial live body weight of 22.55±2.43 kg (mean ± SD). The design employed for this experiment was a randomized complete block design. The animals were grouped into five blocks based on their initial body weight and randomly assigned to five dietary treatments within the block. The dietary treatments used for the study were; untreated teff straw (T1), 250 ml effective microorganism (EM)/ kg treated teff straw (T2), 500 ml EM/ kg treated teff straw (T3), 750 ml EM/ kg treated teff straw (T4) and 1000 ml EM/ kg treated teff straw (T5). All the treatment groups were equally supplemented with a 350g DM /day concentrate mixture. The intake and growth trial experiment lasted for 90 days and the digestibility trial for 7 days. After these two trials carcass parameters were evaluated. The result of this study showed that the CP content of different levels of EM treated teff straw used in the current study was higher than untreated teff straw, but NDF, ADF and ADL contents were lower than untreated teff straw. The total dry matter intake of lambs in T5 (1172.79 g day ) was observed higher value as compared to the lower value recorded in lambs in T1 (773.96 g day ). The apparent dry matter digestibility of lambs in T3, T4 and T5 was significantly (p<0.001) higher than lambs fed untreated teff straw. Average daily body weight gain of lambs in T4 (66 g day ) and T5 (71.56 g day -1 ) was recorded significantly (p<0.001) higher value than the observed lower value lambs in T1 (36.44 g day -1 ). The mean slaughter bodyweight of lambs in T5 (30.27 kg) was significantly (p<0.01) higher than lambs in T1 (28 kg) and T2 (28.4 kg). The highest value of hot carcass weight was recorded at T5 (14.97 kg) in lambs fed a higher level of EM treated teff straw whereas the lowest value was recorded in lambs fed untreated teff straw of T1 (12.3 kg). Dressing percentage as slaughter body weight basis of lambs in T4 (49.48%) and T5 (49.46%) was higher (P<0.05) than lambs in T1 (43.86%). The partial budget analysis showed that lambs in T3 had -1 -1 -1