The main goal of this diploma thesis was the development of fast, selective and sensitive ultra-highperformance liquid chromatography method (UHPLC) used for detection and quantification of impurities, amprenavir and IMP 0.93, in the samples with fosamprenavir calcium as API. Employing Quality by Design approach (QbD) the method development time was significantly reduced and the materials used were saved, which is ecologically more acceptable than traditional way requiring higher consumption of chemicals. The right pH value of the mobile phase was successfully predicted with Marvin Beans software. A new reversed phase UHPLC method with UV detection development was systematically performed using the DryLab® software modelling package where stationary phase, gradient time, column temperature and the pH of the eluent were explored parameters. What DryLab® also includes is a visual presentation of method robust space which allows choosing the right experimental domain where the parameter change would not significantly affect analysis results. Based on the results of DryLab® experiment, the method was developed on Agilent, Zorbax EclipsePlus C18 RRHD (1.8 μm 2.1 x 50 mm) column. Ammonium acetate pH 4 and acetonitrile were used as mobile phases. Optimised gradient method was able to separate fosamprenavir calcium and selected impurities in 3 minutes with the column temperature of 50°C. After the development, validation was conducted according to Q2 (R1) guidelines of International Conference Harmonization (ICH). The developed method was validated with respect to selectivity, linearity, accuracy and precision as well as the solution stability. The limit of detection, limit of quantification and working range were also established. Developed and validated method can be used for quality control of pharmaceutical forms containing fosamprenavir calcium as an active substance.