Quantifying the methane emission from landfills is important to evaluate measures for reduction of greenhouse gas emissions. To estimate methane emission for the entire landfills from 1990 through 2004 in Korea, Tier 1 and 2 methodologies were used. In addition, five different scenarios were adopted to identify the effect of important variables on methane emission. The trends of methane emission using Tier 1 were similar to the disposed waste amount. Methane emission using Tier 2 increased as the degradation of waste was gradually proceeded. This result indicates that disposed waste amount and methane generation rate are the important variables for the estimation of methane emission by Tier 1 and 2, respectively. As for the different scenarios, methane emission was highest with scenario I that the entire landfills in Korea were regarded as one landfill. Methane emissions by scenario III and IV considering different $DOC_F$ values with the waste type and different MCF values with the height of waste layer, respectively, were underestimated compared to scenario II. This result indicates that the method of scenario I employed to most previous studies may lead to the overestimation of methane emission. Therefore, more careful consideration of the variables should be needed to develop the methodologies of greenhouse gas emission in landfills along with the characteristics of disposed waste in Korea.