The interaction of binuclear rhodium(lI) complexes Rh2(OOCCH3)4(H20)2], [Rh2{OOCCH(OH)Ph}2(phen)2(H20)2] {OOCCH(OH)Ph}2, [Rh2(OOCCH3)2(bpy)2(H20)2](OOCCH3)2 and [Rh2Cl2(OOCMe)2(bpy)2](3H20) with ceruloplasmin, cysteine, glutathione and coenzyme A have been investigated using UV-Vis and CD spectroscopies. The complexes containing phen or bpy at pH 7.4 and 4.0 are readily reduced with sulfhydryl compounds, while rhodium(II) acetate is relatively stable in these conditions. Complex [Rh2{OOCCH(OH)Ph}2(phen)2(H20)2] strongly changes structure of ceruloplasmin leading to the decrease of x-helix content and loss of oxidase activity.