The article presents a fragment of the research subject relating to the possibility of decontamination sewage sludges and the method of their conditioning with the use of an ultrasonic field. For experiments, an ultrasonic disintegrator with a frequency of 22 kHz was used. Both primary and digested sludges were tested. Disinfection results were determined based on the qualitative and quantitative analyses of microbes. The greatest noted drop in the number of surviving bacteria took place for an ultrasonic treatment time from 5 to 10 minutes. The aim of sludges conditioning using ultrasounds was to improve the effect of sludges dewatering. The tests involved the selection of a suitable polyelectrolyte and the time of its ultrasonic treatment (sonification) in conjunction with the dewatering parameters of sludges prepared in this particular manner. For a polyelectrolyte dose decreased by half and ultrasonic processed for several seconds, a decrease in the sludges volume by approximately 65% was obtained, as compared with unprepared sludges. At the same time, the microscopic observations of the structure of sludges and polyelectrolytes after the sonification process were conducted.