The primary goal of this thesis was to examine the effect of simultaneous application of mechanical stirring and ultrasound irradiation on borax crystals growth rate dynamics. The cooling sonocrystallization has been conducted in a glass crystallizer with the liquid volume being 2.65 dm 3 and the cooling rate of 6 °C h -1 . Stirring speeds of the SBT stirrer matched the ones required for achieving the state of a complete suspension (N JS ) by Zwietering's criterion, while amplitudes of the ultrasound were as follows: 0, 20, 25 and 30 %.The change of the mother liquor's concentration was determined potentiometrically as well as the change of the absolute supersaturation during above-mentioned amplitudes. According to results, ultrasound irradiation affects absolute supersaturation as well as the change of crystal size during the process. Given the measured sizes of crystals, change in crystal size over time was shown and it is noticeable that continuous sonocrystallization yields averagely smaller crystals. Also, the time required for crystals to attain their final size, effects of both stirring and ultrasound irradiation on the growth rate and the crystal distribution determined by laser diffraction were presented for each amplitude. In general, the time required for attaining the crystalline product of final size extends with an increase of ultrasound amplitude. At the same time, crystal size distribution narrows. Power needed to perform the experiment was also determined. Results suggest that power consumed per unit mass of borax solution by stirring is up to 10 times lower than that of ultrasound irradiation. Considering all obtained results, it can be said that higher ultrasound amplitudes do not imply a more effective sonocrystallization process and therefore, the amplitude of 20 % seems like the optimal one with reasons being that it ensures the shortest time needed for attaining the final size of the crystal as well as not being as costly in terms of energetics as the amplitudes of 25 i 30 %.