This study was carried out to evaluate the effects of microwave irradiated (800 W) soybean meal (irradiated over 5 min) and ruminal protected methionine (Mepron; 3 g/day) on crossbreds Zel weight gain using 15 lambs with an average weight of 31.52±2.32 kg and similar condition score in a completely randomized design with 3 treatments in 5 replicates over 80 days. Three experimental treatements contain untreated soybean meal (T1), microwave irradiated soybean meal (T2) and supplemented with Mepron as treatment 3 (T3). Weight in 15 days and daily feed consumption was determined and dry matter and nutrients digestibility among treatments were compared. Nine of the lamb were killed and their carcasses were evaluated. Daily Dry matter intake (2218.64, 2699.03 and 2775.47 g in T1, T2 and T3 respectively), final body weight (40.08, 50.48 and 52.51 kg respectively in T1, T2 and T3), daily weight gain (135.75, 234.51 and 248 g/day respectively in T1, T2 and T3) and carcasses characteristics between the control treatment and treatments 2 and 3 was significantly different, however there were similar among T2 and T3. The results of current experiment showed that microwave irradiated soybean meal and ruminal protected methionine (Mepron) can significantly improve lamb performance and their carcasses characteristics with increase weight of expensive muscle group (standard muscle groups 1 and 3) and rib eye area.