An important chemical impurity in the composition of zirconium materials for nuclear power engineering is hafnium, the content of which should not exceed 0.05 and 0.01% for domestic and foreign alloy grades, respectively. Hafnium, being an analogue of zirconium in its chemical properties, is difficult to be analyzed using classical methods of analytical chemistry. Among the physical methods, the X-ray fluorescence method is the most expressive, which is important in conditions of continuous production. The method of X-ray fluorescence for measuring the content of hafnium in zirconium-containing material has been tested on the example of potassium fluorozirconate, a precursor for obtaining alloys. With various combinations of crystal analyzers, detectors, and collimators of the wave-dispersive spectrometer, the ratios of the intensities of the analytical lines of Hf and Zr in the second order of reflection were refined, and the degree of decrease in the fluorescence intensity of those lines was determined. The X-ray fluorescence spectra of hafnium lines in potassium fluorozirconate at the content characteristic of nuclear-pure zirconium are studied. The possibility of recording the intensity of the Hf analytical lines and methods of eliminating the interference from the Zr lines in the second order of reflection are considered. The metrological characteristics are calculated for Hf analytical lines. It is shown that the smallest error and the lowest detection limit (0.001%) is provided when using the HfLβ1 line at certain settings of the wave-dispersive spectrometer, including the X-ray tube operation mode, a combination of a crystal analyzer, a detector and a collimator, as well as the amplitude discriminator settings. The method of accounting for the background is recommended. The proposed method of hafnium determination is applicable to the materials with a constant content of zirconium.