Invert syrup is a liquid sweetener, which is produced by sucrose hydrolysis to form fructose and glucose. Important qualitative parameter of invert syrup is the sucrose inversion – weight percentage of invert sugar (sum of fructose and glucose) in invert syrup dry mass. This diploma thesis presents a possibility of sucrose inversion determination by polarimetry in combination with refractometry in invert syrups of 70–78 % dry mass produced at 80 °C and pH 2,4. New relationship describing the sucrose inversion as a function of polarization and refractometric dry mass was determined. The results of sucrose inversion determined using this new relationship were compared to results obtained by HPLC/RI, which was used as a reference method. The difference between these 2 determination methods was 0,1 ± 0,5 %. The new relationship was detemined with reference to the fact, that under the processing conditions, more glucose than fructose is formed. The fructose : glucose concentration ratio formed under processing conditions was observed to be equal 0,96 ± 0,02.