Two bacterial fermentation products containing amylase were added singly or combinationally to waste activated sludge (WAS). Biochemical methane potential (BMP) experiment of enzyme treated sludge was carried out to investigate the effects of amylase, which could be released by WAS, on the digestibility of sludge. The results show that enzymatic pretreatment can facilitate the hydrolyzation of macromolecule organic matters into small molecular organics, with a 56％ increase in volatile fat acids. For treated sludge, the volume occupied by particle between 200～2 000 μm decreased obviously. Although the hydrolyzability of sludge is low, the digestibility of pretreated sludge was remarkably improved. The reduction of volatile was enhanced from 36.02％ to 42.19％. The specific methane yield was 434 mL CH₄ per gram volatile solid removed, which was higher than that of untreated sludge (381 mL/g).