Na2[Fe(CN)5NO]. 2H2O contains cyanide ligands that cannot be so easily replaced chemically. An effort has been made to substitute this ligand by another anionic ligand like malonate (bidentate ligand). The progress of this photochemical reaction has been observed spectrophotometrically and the product was isolated and characterized. The effects of different parameters like pH, intensity of light concentration of sodium nitroprusside and ligand concentration on the yield of this substitution product have been studied. A tentative mechanism for this reaction has been proposed.