Abstract: Influence of acrylate and p-toluenesulfonate on methane-producing activity with acetic acid or propionic acid as substrate was investigated. It was indicated that inhibition of methane-producing activity by both acrylate and p-toluenesulfonate with propionic acid as substrate is more significant than that with acetic acid as substrate. The semi-effective (EC₅₀) concentrations of acrylate for inhibition of methane-producing activity with acetic acid and propionic acid as substrates were 717 and 235 mg/L, respectively. There was no significant inhibition effect on methane production with acetic acid as substrate by p-toluenesulfonate below 10 000 mg/L, while the semi-effective concentration for inhibition of methane-producing activity with propionic acid as substrate was 9 500 mg/L. When acrylate and p-toluenesulfonate coexisted in the system, no significant synergistic effect was observed on inhibition of methane-producing activity.