This study aimed to investigate the methanotrophic activity and its response to global warming with different enclosure time. We chose typical grasslands in Xilin River Basin of Inner Mongolia, China to investigate the methanotrophic activity at 18 °C and 28 °C under different enclosure treatments: 79E (grassland enclosed since 1979), 99E (grassland enclosed since 1999) and G (freely-grazed grassland). The main methods included laboratory incubation experiment and the collection of CH_4 flux data. The results showed that at 18 °C, the methanotrophic activity was 0.032 mug g~(-1) h~(-1) for 79E, 0.0 12 mug g~(-1) h~(-1) for 99E, and 0.024 mug g~(-1) h~(-1) for G. At 28 °C, the methanotrophic activity was 0.042 mug g~(-1)h~(-1), 0.031 mug g~(-1) h~(-1) and 0.055 mug g~(-1) h~(-1), respectively. The methanotrophic activity of 79E was found to have the lowest sensitivity to temperature change, while 99E had the highest one. The methanotrophic activity in all three treatments increased along with the temperature. Taking into account the methanotrophs potential and comparing the in situ CH_4 fluxes, we concluded that grassland can remove more CH_4 under the future global warming trend.