An intracellular endo-cellulase was isolated and purified from the fermentation of Aspergillus niveus MA35 in the gut of Megalobrama amblycephala. The enzyme was purified sequentially by Q-Sepharose Fast Flow chromatography and Sephadex G-100 gel chromatography. The specific activity of the purified endoglucanase increased to 30.6 U/mg from 22.3 U/mg of the crude endoglucanase. The molecular masses of the enzyme was determined by SDS-PAGE to be about 45 ku. The optimum temperature is 45 ℃ and the optimum pH is 4.5. The enzyme has good stability between pH 4.0-8.0 and 30-55 ℃. Zn²⁺ and Mn²⁺ have an activation effect on enzymes. Mg²⁺, Cu²⁺, Fe²⁺, Cd²⁺ and Co²⁺ have inhibitory effects on enzyme activities, among which Mg²⁺, Cu²⁺ and Fe²⁺ have strong inhibitory effects, and Na⁺, K⁺ and Ca²⁺ have little effect on enzymes.