Abstract: Wheat straw is one of the livestock feeds in Saudi Arabia. However its use as feed is rather limited because of its low crude protein content. This trial was undertaken to improve the protein content of wheat straw by urea treatment. Twenty-five wheat straw samples (each weighing 3 Kg) were sprayed with five different urea solutions at the rate of 40 mL of water/100 g of straw. The solutions were prepared by dissolving 1, 2, 3, 4 or 5 g of urea in 40 mL of water. The five treated samples at each urea level were kept in air tight containers and assigned at random to storage at 30 C for 2, 4, 6, 8 or 10 weeks. Subsequently, proximate chemical° composition of treated and untreated straw was determined. Analysis of variance was used to examine the effect of urea treatment, ureolysis duration and their interaction on crude protein. All sources of variations affected (p<0.001) crude protein of treated straw. The highest crude protein content (ranging from 8-11% as compared with a mean of 6.67�1.9% for the control) was obtained on the 4 g of urea/100g straw dissolved in 40 mL of water for all storage periods. Different mathematical models were used to describe changes in crude protein content of treated straw with advancing storage period. The fifth polynomial level provided the best fit for that relationship. Lambs preferred (p<0.001) urea-treated to untreated straw and treated wheat straw was equally (p>0.05) preferred to Rhodes grass.