Abstract:CH4 uptake were compared after grassland and cropland soils in the agro-pastoral ecotone of Inner Mongolia over three growing seasons (2008~2010). Four adjacent sites with different land-use histories were selected, including grassland (reference site) and cropland 5, 10 and 50 years after conversion. The flux measurements were obtained using a closed-chamber method and were performed continuously from April to October in 2008, 2009 and 2010 in study site. The results showed a significant difference in CH4 uptake between cropland and grassland in 2008 (FCH4=273.7, P<0.001), 2009 (FCH4=264.8, P<0.001) and 2010 (FCH4=362.4, P<0.001). Grassland had the lowest CH4 uptake values of 141.4mg/m2, 210.0mg/m2 and 236.0mg/m2 in the 2008, 2009 and 2010 sampling seasons, respectively. The cumulative CH4 uptake of cropland soil increased by 20%~280%, compared with the grasslands from 2008 to 2010. Decreased cumulative CH4 uptake was observed with an increase in cropland age from 5 to 50 years. CH4 uptakes were negatively correlated with soil NH4+-N (R2=0.7380, P<0.01) and soil moisture. Our study indicated that CH4 uptake existed obviously differences among the sites during 3 growing seasons and the soil physical-chemical properties drive these differences.