Effects of inoeulum on mid-temperature anaerobic fermentation of sweet potato lees were studied. Gas production rate, pH value, amino nitrogen (NH4^+ -N), volatile fatty acid (VFA) content, percentage of methane and reduction of TS and COD affected by four different inoculum at 45℃ were studied. The results showed that, with increase of inoculums, the accumulation of microorganisms shortened, peak of gas production brought forward and gas production period shortened, and moreover, the pH buffer capacity of fermentation system was improved...