The refuse derived fuel (RDF) is available for renewable energy which can use alternative fuel to utilize recycling municipal solid waste (MSW). The RDF plant where can produce 100 ton/month of RDF, the largest manufacturing plant in Korea so far, were investigated in this study. The actual operated RDF yield showed 21.7% that was lower than expected yield; originally designed value was 25.0% in this plant. The cause of these results was that difference between physicochemical properties of MSW applied this plant originally and actual incoming it. The MSW affected to make separation efficiency of MBT process decreasing. It led to reduce amount of combustible material which needed for RDF after separating process. The each element of facilities was modified; decreasing width of the blade of a shadder from 110 mm to 63 mm, reducing the size hool of trommel screen to possible separating under 40 mm of MSW, increasing heat capacity of dryer from 2,000 Gcal/hr to 2,500 Gcal/hr, and conveyor type changed to prevent path MSW away during moving into each process and so on. After modifying facilities, got more combustible materials which were once lost and RDF yield increased to 30.9%. Whereas, low heating value of RDF was 4,725 kcal/kg, 0.8% of chlorine on average and other parameters were satisfied with domestic standard of RDF regardless of modifying MBT facilities.