Abstract: The solid complexes of uranyl and thorium nitrates with 2-(5-bromo-2-py-ridylazo)-5-diethylaminophenol(5-Br-PADAP) have been synthesized in acetone medium. Composition of complexes are determined by elemental analysis as following: UO2(NO3)2(HL)2;Th(NO3)3 L·HL (HL = 5-Br-PADAP). The complexes have been characterized by infraed spectra, ultraviolet-visible spectra, solubility and molar conductance determination, thermogravimetric(TG) and differential thermal analysis (DTA), and X-ray powder diffraction.