Sodium nitroprusside contains cyanide ligands that are not easily replaced chemically. Studies on its substitution reaction with another anionic ligand iodide, chloride, bromide and fluoride'' are reported here. The rate of this photochemical reaction has been studied spectrophotometrically. The effect of different parameters like pH, intensity of light, sodium nitroprusside and [iodide, chloride, bromide and fluoride] ion on the reaction has also been studied. The product has been isolated and characterized by different analytical methods. A tentative mechanism for the photochemical substitution reaction is also proposed.