Three new double complex salts (DCSs) containing [Pt(NO3)6]2- anion and Rh(III) metalorganic cations [Rh(4-pic)4Cl2]2[Pt(NO3)6] (1,4-pic = 4-methylpyridine), [Rh(bpy)3]2[Pt(NO3)6]3 (2, bpy = 2,2′-bipyridiine) and [Rh(bpy)3][Pt(NO3)6](NO3)(CH3COCH3)(CH3CN)(H2O) (3) were prepared and characterised by elemental analysis and infrared spectroscopy. Crystal structures of 1 and 3 were determined using X-ray single crystal analysis. Thermal decomposition of salts 1 and 2 in various atmospheres (He, He/H2, air) was shown to yield Rh–Pt solid solutions with a Rh:Pt ratio inherited from the starting salt composition. The Rh0·67Pt0·33/CeO2 catalyst was prepared by thermal decomposition of salt 1 supported on a CeO2 surface. The catalyst was tested in a CO oxidation reaction and demonstrated full conversion of CO from about 145 °C at gas hourly space velocity of 200 000 ml g−1 h−1.