The reaction of uranyl nitrate with the [P8W48O184]40– polylacunary polyanion gives the [(UO2)7P8W48O184]26– (1) and [(UO2)8P8W48O184]24– (2) anions, which were isolated as potassium and ammonium salts. For K24[(UO2)8P8W48O184] · 50H2O · 3LiCl and (NH4)16H8[(UO2)8P8W48O184] · 50H2O, X-ray diffraction study was performed. The incorporation of uranyl ions into [P8W48O184]40– was confirmed by IR and Raman spectroscopy and by mass spectrometry. Electrochemical study of 2 indicated the possibility of uranium reduction to U(IV). X-ray luminescence of the potassium salts of 1 and 2 was investigated.