A log of waste oak wood collected from a Korean mushroom farm has been tested for ammonia percolation pretreatment. The waste log has different physical characteristics from that of virgin oak wood. The density of the waste wood was 30% lower than that of virgin oak wood. The difference is possibly due to the biodegradation done during the mushroom cultivation. However, there is little difference in the chemical compositions between the woods. Due to the difference in physical characteristics, the effects of the pretreatment conditions were also quite different. While the optimum temperature was determined to be 100^oC for waste oak, the optimum pretreatment was possible at 150^oC with virgin oak wood. Presoaking for 12 hours with ammonia solution before pretreatment was helpful to increase the delignification efficiency. The enzymatic hydrolysis yield of the pretreated waste oak is even higher than that of pure cellulose with the same enzyme loading. Detailed experimental results will be presented.