By the application of the spectrophotometric methods the composition of the complex and by the pH-metric method the reaction of complex formation in 70% ethanol, were determined. It was found that a complex WO3(C15H9O3)22-whose concentration stability constant β2ranged from 16.45 at pH 4.0 to 11.47 at pH 7.0, was formed. Conditions were investigated for the spectrophotometric determination of 3-hydroxyflavone by means of the reaction of complex formation. It was established that in 50% ethanol 3-hydroxyflavone can be determined with great accuracy in quantities from 0.05 to 0.30 mg/ml. All investigations were carried out at room temperature (20°C) and constant values of pH and ionic strength.