Since last decades, much interest has been evidenced for bioconversion of lignocellulosic materials such as production of edible mushroom. In Iran, the mushroom industry has been expanded during the last 20 years and currently more than 50000 tons of mushroom compost is produced annually by aerobic fermentation system. The compost remained after cropping of mushroom constitutes a potential pollutant and its disposal increases the production cost. This waste material is usually rich of microorganisms and extra cellular enzymes (Ball and Jacksa, 1995) and contains a high level of nitrogen, calcium, phosphorus and trace elements and more degradable than the original straw in the rumen (Zadrazil, 1997). However, there are limited information regarding the nutritive value and utilisation of the mushroom spent straw in animal nutrition. This experiment was conducted to study the nutritive value and acceptability of the Agaricus bisporus mushroom spent wheat straw, obtained from bag system mushroom growing in sheep nutrition.