Chemical recycling (chemolysis) enables complete depolymerization of poly(ethylene-terephthalate) to monomers or partial depolymerization to oligomers. One of the methods of chemical recycling is hydrolysis. Hydrolysis of PET produces terephthalic acid and ethylene glycol. The aim of this thesis was to investigate the effects of temperature, reaction time and quantity of used chemicals on the degree of depolymerization of PET while conducting base catalyzed hydrolysis. Eight reactions, with different combinations of laboratory conditions, were conducted. The PET sample that was used came from blue waste bottles, and the reactions were catalyzed with sodium hydroxide. A weight percentage of oligomers, ethylene glycol and disodium terephthalate, in relation to the weight of the PET sample, was calculated for every sample after a conducted reaction. Every sample was also characterized by FTIR spectroscopy and thermogravimetric analysis. The results show that with the increase of temperature, increase in quantity of the catalyst and prolongation of reaction time, the mass fraction of the depolymerized initial sample increases. It takes 2 hours of hydrolysis in 50 ml of EG and 0.5 g of NaOH at 190 °C to completely depolymerize 1 gram of PET. TGA and FTIR spectroscopy proved the depolymerization of PET and getting the products that were expected.