Abstract: A sensitive and selective RP-HPLC method for the determination of doxofylline(D)and its related compounds has been developed. Chromatography was carried out on a YWG C₁₈column, and acetonitrile-phosphate buffer(0.62 mol·L^-1,pH 5.4)in the ratio of 15∶85 wasused as the mobile phase,Absorhance at 274 nm was monitored.Theophylline(T)and otherimpurities were directly determined by the peak area, whereas D was quantitated by an internalstandard method, caffeine was used as the internal standard.The detection limlts of D and T were1ng and 0.6 ng,respectively.