Production of methane from paddy fields and the related archaeal community are both influenced by environmental factors and soil characteristics of the field (e.g. pH, carbon and nitrogen contents). To study the effect of soil pH on methane production and community structure of the methanogenic archaea at high temperature, two soil samples S1 (pH 7.88) and S2 (pH 4.67) developed from different matrices were anaerobically incubated at 50 ℃ for 100 days. Methane production was measured continually by gas chromatography during the incubation. Soil characteristics, such as pH, organic carbon and ammonium nitrogen contents were also evaluated in the supernatant or the soil itself. The variations in the microbial structure with incubation time in the two soils were studied by terminal restriction fragment length polymorphism (T-RFLP) analysis based on archaeal 16S ribosomal RNA gene. The results showed that the organic carbon content decreased with the formation of methane during incubation, whereas the variation of ammonium was similar in both the supernatants and soil samples S1 and S2. Although the final amount of methane produced was same for S1 and S2, the changes in pH and methane production rates were significantly different between the two soils. It was found that the rate of methane formation increased with the increase of pH. The T-RFLP profiles showed that Methanosarcinaceae and Methanocellaceae were the primary active methanogenic groups in paddy soil at 50 ℃. Analysis of the entire T-RFLP profiles via twodimensional plots of PCA (principal component analysis) revealed that the developmental direction of structures of the archaeal populations in the two soils were different. Acidic paddy soil was more suitable for enhancing the activity of Methanocellaceae.