Nanoparticles have recently emerged as efficient hetrogeneous nanocatalysts in the organic synthesis. However, particles with diameters of less than 100 nm are difficult to separate by filtration techniques. This drawback can be overcome by using magnetic nanoparticles (MNPs), which can be easily removed from the reaction mixture by magnetic separation. Magnetic nanoparticles are efficient, readily available, high-surface-area resulting in high catalyst loading capacity and outstanding stability heterogeneous supports for catalysts. The catalyst has been characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) and we present for the first time catalytic applications of magnetic nanoparticle-supported sulfamic acid (MNPs-PSA) as a novel magnetically heterogeneous nanocatalyst for Synthesis of Phthalazine Derivatives. In summary, the notable advantages of this method are easily separation of nanocatalyst by with the assistance of an external magnetic field from the reaction mixture and reused for several consecutive runs without significant loss of their catalytic efficiency