The aim of this study was to investigate the effect of gamma-radiation on the degradation of doxazosin (a widely used antihypertensive drug) in aqueous solution. The research was conducted at the Radiation Chemistry and Dosimetry Laboratory, Division of Materials Chemistry, Ruđer Bošković Institute. The efficiency of degradation was studied under different absorbed doses, dose rates, pH values and in the presence of radical scavengers and inorganic ions. The irradiated samples were analyzed by UV/VIS spectrophotometry and high performance liquid chromatography with diode array detector. It was found that •OH are the main reactive species responsible for the degradation of doxazosin, the efficiency of degradation being higher with increasing dose of gamma radiation. The presence of nitrates had a stronger effect on doxazosin degradation compared to carbonates and phosphates. An optimal pH for doxazosin degradation was in the neutral, slightly acidic range (pH = 6.5), while degradation was slower under extremely acidic or alkaline conditions. It was found that the degradation of doxazosin in well water was much slower compared to ultrapure water, suggesting that organic and inorganic components dissolved in natural waters influence the efficiency of radiolitic degradation of doxazosin.