Cerium(IV), Thorium(IV) and Uranyl(II) complexes with the ammonium salt of sulfasalazine drug (H2SSZ, HL-) have been studied. The structures of the complexes were elucidated using elemental analysis, IR and mass spectroscopy and thermal analysis. The complexes were isolated in 1:1 and 1:2 (M:L) ratios. The solid monocomplexes (1:1) (M:H(2)SSZ) were isolated in the general formulae [UO2(L)(H2O)2].2H2O and [M(L)(X)z(H2O)n].yH2O (M=Ce(IV) and Th(IV) (X=NO3, z=2, n=2, y=0-3)). The biscomplexes (1:2) (M:H2SSZ) solid chelates found to have the general formulae [UO2(HL)2].2H2O and [M(L)2(H2O)2] (M=Ce(IV) and Th(IV)). The thermal decomposition of the complexes should be discussed in relation to structure, and the thermodynamic parameters of the decomposition stages were evaluated applying Coats-Redfern and Horwitz-Mitzger methods.