Abstract Soils of three sites were studied in the Inner Mongolia steppe; one site non-grazed for 26 yr (NG26), another site non-grazed for 6 yr (NG6) and a third site freely grazed all along (FG). The composition of methantrophic communities was characterized by pmoA gene fragments (coding for a subunit of particulate methane monooxygenase) that were PCR amplified from total soil DNA extracts, using denaturing gradient gel electrophoresis (DGGE) method. Cluster analysis based on the DGGE band patterns indicated that the methanotrophic communities structure of NG6 and FG soils were similar to each other but different from that of NG26 soil. Sequence analysis showed that most bands belonged to the cluster of USC γ. This is the first report that USC γ cluster is dominated in the grassland soil.