Tow experiments were conducted to evaluate the effect of alkali treatment on the wheat straw. In experiment 1, chopped wheat straw (0.5 – 1.5 cm) was subjected to different alkali treatments involving 3 levels of urea (T₁) (1.5, 3 and 5 % w/w), 3 levels of lime (T₂) (4, 6 and 8 % w/w) and a combination of urea and lime (T₃) (5% urea plus 4 or 6 or 8% lime w/w). The moisture in all treatments was 50% and the treatment period was 4 weeks. Cell wall constituents (CWC) solubilised significantly (P<0.05) due to synergistic effect of alkali treatment. Wheat straw was treated with 5% urea plus 8% lime has the lowest CF, NDF, ADF and ADL being 31.61, 53.54, 44.29 and 5.38%, respectively compared with untreated wheat straw (40.66, 76.14, 54.81 and 9.21%) in the same order. The average of crude protein increased in T₁ and T₃ by 114.5 and 163.1 %, respectively compared with untreated wheat straw. Data indicated that a combination of 5 % urea plus 8 % lime at 50 % moisture for 4 weeks reaction time was the most effective treatment for reducing the ADF, ADL and hence improving the chemical composition of wheat straw.                 In experiment 2, growth trials for 90 days were conducted by using 12 growing Rahmany lambs (averaged 24.10 kg body weight and 7-8 months old). Animals were divided randomly into two groups and were fed at 3 % of live body weight on ration consisted of 75% concentrate mixture and 25 % roughage. In first group (control, R1), the roughage was berseem hay, while, in the other group (R2) it was alkali treated wheat straw, 5 % urea plus 8 % lime at 50 % moisture for 4 weeks reaction time. There was no significant (P<0.05) difference between R1 and R2 in the digestibility of OM (84.74 and 83.77 %) and NFE (88.35 and 87.66%), respectively. The digestibility of CF was higher in R2 (70.95%) than in R1 (67.80%).  The nutritive values of the experimental rations as total digestible nutrient (TDN) and digestible crude protein (DCP) were 99.48 and 103.98% in R2 as a percent of R1.                 There was no significant (P<0.05) difference in average daily body weight gain, total body weight gain and final body weight between the animals fed the experimental rations being (141.11 and 130.0 g), (12.7 and 11.7 kg) and (36.8  and 35.8 kg) in R1 and R2, respectively. So, berseem hay can be replaced by wheat straw treated with 5 % urea plus 8 % lime at 50 % moisture for 4 weeks incubation period, without any adverse effects on growth performance of growing lambs.