Currently, researchers are highly fascinated to the synthesis of nanoparticles, especially magnetic nanoparticles using biological materials. In the present research, synthesize of iron magnetic nanoparticles was done by using S.adnata Desv leaf extract as a reducing agent. Magnetic FeNP was synthesized by co-precipitation of ferric chloride and ferrous sulfate. The formation of black colored precipitate indicates the development of magnetic iron nanoparticles. The crystalline nature of the particle was analyzed by XRD and the size was 16.7 nm, functional group and capping agents were identified through FTIR and the results confirmed the synthesis of nanoparticles. The magnetic nature was authenticated by external magnetic force. The size and morphology of the particle were analyzed by SEM-EDS system. The nanoparticle was utilized for the decolorization of reactive- Blue FBS dye solution. Complete decolorization was obtained by the magnetic nanoparticles in acidic pH. This work proved the decolorizing efficiency of green synthesized magnetic nanoparticles.