A field research at Sudokwon landfill was carried to analyse the effect of leachate and organic waste water injection on decomposition characteristics of landfill waste. The moisture content after leachate (79,783 m3) addition into block 3A for 1 year increased from 27.4% to 34.1%. As a result of moisture increasement, Cellulose and Lignin proportions as indicators of waste degradability changed from 1.45 to 1.18. It is also illustrated that TOC as an indicator of CH4 production potential reduced from 22.0% to 19.5%. Comparison results of TOC after 4 months of each leachate, digested waste water, food waste water injection into block 4A shows reduction of 3.5%, 4.7% and 3.7%, respectively. Hence, it is indicated that injection of leachate and organic waste water into landfill enhances the rate of CH4 production as well as the speed of landfill stabilization.