This experiment was conducted to evaluate the feed value of rice straw fermented with yeasts and waste sawdust after shiitake culture(WSSC). Nutrients disappearance and degadability rates of the rice straw were analyzed. Three different types of feeds were formulated. 1) Rice straw was mixed with WSSC, cam and molasses at the ratio of 1 :0.067 :0.18:0.02. This formula was used for control. 2) The mixture of rice straw, cam and molasses was anaerobically fermented at 30℃ for 6 days, and then WSSC was added (anaerobic treatment). 3) After WSSC addition into the pre-fermented mixtyre, two weeks of aerobic treatment period were provided (aerobic treatment). Korean rattles (Hanwoo) were used for in situ experiment. The results obtained from this research are as follows : 1. The contents of neutral detergent fiber(NDF), acid detergent fiber(ADF), cellulose, and crude protein(CP) in the aerobic treatment increased, while hemicellulose content clearly decreased, when compared to the control. However, chemical compositions of anaerobically treated diet were similar to those of control. 2. Lower dry matter(DM) disappearance in the rumen was occurred in the anaerobic treatment. The DM disappearance rates at 6 and 12 hours after feeding in the aerobic treatment were lower than those in control, but significantly increased from 24 hours after feeding. 3. The NDF disappearance rate was the lowest in the anaerobic treatment, and NDF disappearance rate in the aerobic treatment significantly increased from 24 hours after feeding. 4. When compared to the control, the ADF disappearance rate ip the anaerobic treatment was similar, but ADF disappearance rate in the aerobic treatment was greater. 5. Degradation rate of DM, NDF, and ADF in the rumen increased in the aerobic treatment, compared to the anaerobic treatment and control. Effective degradability of ADF was found to be higher in the aerobic treatment than that in the control by obtaining 9.4, 6.3, and 4.8% at K (passage rate) of 0.02, 0.05, and 0.08, respectively.