The purpose of this study was to observe the ultrasound working principle and to examine the influence of ultrasonic amplitude on the size of borax crystal obtained by the controlled cooling in the batch stirred crystallizer. In the first part of the study, batch crystallization was carried out in a stirred reactor from a solution saturated at 30 ° C and cooled at 6 ° C h -1 . Concentration change of the mother liquor over process time was measured in order to determine the onset of nucleation and the change in the concentration due to crystal growth. Upon the completion of the process, sieving and granulometric analysis of the product was done. In the second part of the work, the effect of ultrasound amplitude on three classes of crystals obtained in a batch stirred reactor was examined. The classes of crystals of average size 45, 170 and 375 m were ultrasonically suspended in a solution of acetone saturated and thermostated at 25 ° C. Ultrasound amplitude was 20, 30 and 40%. After 10, 20 and 30 min of ultrasonic treatment, the granulometric properties of the crystal were analysed by laser diffraction method. At the same time, with the measurement of the crystal size, the electrical conductivity of the solution, , was measured in order to monitor concentration change within the solution. The results of the study showed negligible change in size of examined crystal classes over process time at the applied ultrasound amplitudes. Also, the conductivity of the solution has not changed, which indicated that applied amplitude will not cause breakage or dissolution of the borax crystals and can be used in the further study of influence of ultrasound on the crystallization kinetics of borax.