The objective of this investigation was to study the effectiveness of applying ultrasound field for enhancement of biological treatability of leachates generated in a typical municipal solid waste sanitary landfill. The sonification of the leachate was carried out in static condition using the disintegrator UD-20, the field frequency of 20 kHz and different amplitude in the range of 8-16 mu m. A laboratory-scale sequencing batch reactor (SBR) was used for the examination of ultrasound application. The effect of different sonification parameters on the efficiency of this biological treatment process was studied to optimize performance, especially for the removal of nitrogen compounds and organic matter. Because of the high variability of the landfill leachate used in experiment, unsteady treatment efficiency was observed. It was found that, ultrasound pretreatment of raw leachate resulted in improvement of the treatment efficiency. The results show significant improvement of the removal rates of COD and nitrogen compounds in reactor operated with leachate irradiated by ultrasound. It could be explained by the fact that an ultrasound wave in liquid causes the periodical compression and rarefaction of the medium.