The main challenge in the formulation of pharmaceutical oral dosage forms lies in the low bioavailability of the drug, which is most often attributed to its poor solubility. Selection of solubility improving method depends on drug property, site of absorption, and required dosage form characteristics. The aim of the work described in this thesis is to increase the solubility of the active substance, celecoxib, by using hot melt extrusion (HME) technique. To obtain extrudates, in the experiment were used Soluplus, poly(ethylene glycol) (PEG) and celecoxib as the active substance. Mixtures were prepared and extrudates were obtained at certain temperatures (CLX-SOL-170, CLX-SOL-120 and CLX-PEG-57-61). The prepared samples were analysed for their content, solubility, release profiles and characterized by DSC and XRD methods. Solubility was measured by using the so-called shake-flask method and tested by using UV/Vis spectrophotometer. In vitro testing of celecoxib release was studied in USP 2 device under prescribed conditions. All substances used, physical mixtures and extrudates were analyzed by using DSC and XRD characterization methods. By applying DDSolver, an Excel add-in software package, i.e. the pairwise comparison method – the release profiles of the active substance were compared by using the similarity factor and the difference factor. The results showed that solubility and release rates of celecoxib successfully increased. In conclusion, according to the results obtained, it was shown that the highest solubility was achieved with Soluplus at the extrusion temperature of 170°C (CLX-SOL-170). To confirm this, the amorphous structure of the resulting extrudate, which directly affects the solubility, was determined by using XRD methods.