This research investigates the feasibility of the venturi cavitation system (VCS) for the sludge pretreatment to increase biodegradability. The performances of the VCS depended on the inclination angle of the venturi outlet, and better results obtained with 12° than with 8° or 15°. Although it is energy efficient to use several venturies in series, the number of the venturies should be determined with detailed fluid dynamic calculations. The linear relationship between total solid (TS) concentration and the increases in soluble chemical oxygen demand (ΔSCOD) was observed for both wasted activated sludge (WAS) and primary sludge, which might be related to the better conditions for cavitation development at high TS concentrations even with higher viscosity. The VCS achieved better energy efficiency in terms of ΔSCOD/kJ compared to high-speed homogenizer (HSH). On the other hand, the VCS showed a similar energy efficiency for mixed sludge with 1.8% TS, but lower efficiency for WAS with 4% TS when compared to ultrasonic disintegration.