The aim of the present work was to develop a method for assaying afobazole in substance and medicinal formulations for assessment of the contents of both technical contaminants and likely degradation products. Studies were performed using HPLC on a liquid chromatogram with a spectrophotometric detector in the following conditions: a Phenomenex column (250 × 4.6 mm, sorbent Luna C18(2), 5 μm); mobile phase: acetonitrile, methanol and 0.02 M potassium hydrogen phosphate pH 7.3 solution at a ratio of 100:100:240 (by volume). A method was developed allowing separation of afobazole and its initial and intermediate synthesis products, oxidation products, and other afobazole degradation products produced in acidic and alkaline media and on oxidation and exposure to sunlight. This method yields data on the stability of the substance and medicinal formulations both during preparation and on storage.