In the paper the problem of excessive sludge anaerobic stabilization process intensification by combined pretreatment method i.e. alkaline hydrolysis and ultrasonic field active action was discussed. Combination of the mentioned methods, base on different mechanisms of action allow to obtain high pretreatment efficiency i.e. essential increase of sludge disintegration degree and the course of sludge anaerobic stabilization process. The fermentation processes having periodical character were conducted in the laboratory scale in the mesophilic conditions in the eight laboratory bulbs being models of fermentation chamber as well as in the fermentation chamber of Applikon. Process of alkaline pretreatment was conducted in the ambient temperature, in the time of 24 h and in the hermetic plastic bottles of 5 dm(3) volume. The following solid hydroxides were applied: Mg(OH)(2), Ca(OH)(2), KOH and NaOH. The supersonic disintegrator UD-20 (TECHPAN Warsaw, Poland) was used, with a ceramic transducer and power output of 180 W. The used waves has the frequency of ca. 22 kHz. Applied sonification time was of 30 divided by 480 s and the vibration amplitude was of 8 divided by 16 mu m. In anaerobic stabilization process of excessive sludge after alkaline pretreatment aided with ultrasonic field for about 2-time increase of volatile solids reduction was obtained. Sludge pretreatment intensified the biogas production of about 4-time, as compared to untreated sludge. The connection of alkaline hydrolysis and active ultrasonic field action has influence on the high effectiveness of excessive sludge stabilization process.