A simple, rapid and accurate RP-HPLC method was developed for the determination of doxofylline and photolytic degradation product. The method showed a linearresponse for concentrations in the range of 1-200 ìg/ml using acetonitrile: formic acid (90: 10); pH-3.0 as the mobile phase with detection at 274 nm and a flow rateof 1 ml/min and retention time 2.9 min. The method was statistically validated for accuracy, precision, linearity, ruggedness, robustness, forced degradation, solutionstability and selectivity. Quantitative and recovery studies of the dosage form were also carried out and analyzed; the % RSD from recovery studies was found to be lessthan 1. Due to simplicity, rapidity and accuracy of the method, we believe that the method will be useful for routine quality control analysis. The photolytic degradation product as well as pathway was characterized by LC-MS/MS.RESULT AND DISCUSSIONA sensitive, selective, precise and accurate highperformance liquid chromatographic method ofanalysis of doxofylline in both as bulk drug and in formulation was developed and validated. The mobile phase consisted of acetonitril:0.05M formic Acid (90: 10v/v); pH-3.0. The detection wavelength was 274nm. Thissystem was found to give the sharp peak for doxofylline (RT-2.9). The method was validated as per ICH guideline. Stability indicating assay method in which photolyticstress condition was used for quantitative estimation of doxofylline in tablet formulation and identification of photolytic degradation product The separation of drug from its degradation product were optimized by varying the ratio &/or nature of organic modifier. Finally method was developed using same mobile phase composed of acetonitrile: formic acid (90: 10); pH-3.0, in that both drug and degradation product showing good elutionRT-2.9 (Doxofylline) and RT-4.7 (Photolytic degradation product) and m/e-413 (Dimer).The photolytic degradation product and pure drug were identified by LC-MS/MS in order to establish photolytic degradation pathway.