Abstract: The Cu/γ-Al₂O₃ catalysts with 11.32% copper contents prepared by the incipient wetness impregnation were tested in a fixed bed reactor. The effects of SO₂ concentration (0 ~ 0.02%) on the combustion characteristic and stability of low concentration methane (3%) over Cu/γ-Al₂O₃ catalysts were investigated. By the analysis of microstructure and chemical component of fresh and aged catalysts, the mechanism of sulfur poisoning in the catalytic reaction was discussed by combining with the theoretical analysis. The results show that the addition of SO₂ in the feed gases leads to a decrease of activity and stability of the catalysts. The methane conversion decreases rapidly with the increasing concentration of SO₂. The results of SEM, EDS, FT-IR and XRD reveal that the presence of SO₂ in the feed gases can result in agglomeration and accumulation of sulfur on the surface of Cu/γ-Al₂O₃ catalysts. Sulfur is in the form of sulfate, which mainly contains copper sulfate (CuSO₄). Under the condition of oxygen enrichment, the copper sulfate produced by the absorption of SO₂ and oxygen ions on Cu²⁺ is attached to the surface of catalysts and forms a hard shell, which is the major reason for the sulfur poisoning.