Each year, agriculture generates large amounts of lignocellulosic waste of low nutritional quality. This quality could be improved by the use of basidiomycetes. The aim of this study was to characterize the bedding residue from commercial cultivation of Agaricus bisporus as a feed for ruminants. Nutrient analyzes and mycotoxins content were performed. In situ degradation kinetics and in vitro gas production were also determined. The ash content decreased 9% and crude protein increased by 2.7% when the cover soil (peat) was removed from the bedding residue. In vitro degradability of dry matter at 72 hours was 8.4%. The peat-free bedding residue had 12.7, 29.1, 26.1, and 39.6% CP, NDF, ADF, and ash, respectively. This material contains most of the minerals required by cattle. A 76% of the nitrogen fraction is insoluble in borate-phosphate buffer, and 83% of the total nitrogen is of proteic nature. No detectable restrictive levels of mycotoxins were found. The ruminal DM effective degradation (DE) of the peat-free residue was 39.6%. This is 68% higher than the residue with peat for the time and accumulated gas at the inflection point and at the maximum gas production rate. The high content of sulfur (2.1%) in the peat-free residue might limit its dietary inclusion for cattle to a maximum of 14%.