The article handles two related subjects. First, it’s the study of forced-acid/heat degradation of phenazopyridine HCl (PAP). The reaction pathway was evidenced with different criteria. A three wavelengths-based reversed phase HPLC method with an isocratic mobile phase system (acetonitrile:acetate buffer of pH 4, 1:1, v/v) was developed as a stability-indicating assay of particular application for simultaneous determination of PAP and its related degradation products/impurity. The analysis time was less than 8 min at a flow rate of 1 mL min-1. The detection and quantification limits of degradation products/impurity were in the ranges of 0.02-0.1 and 0.06-0.3 μg mL-1, respectively. The impurity profile of PAP in drug substance and tablets was investigated and could be determined down to a level between 0.03% and 0.005%. The second subject deals with establishment of spectrofluorimetric method for quantification of phenol (PH) and 2,6-diaminopyridine (DAP), as degradant/impurity in PAP, at trace concentrations. The method is based on measurement of the native fluorescence in acidic ethanol solution (DAP) or in aqueous acidic solution (PH). The method was applied to check the purity/stability of PAP in drug substance and in tablets dosage form.