|Abstract For the first time, the design and preparation of magnetic polyvinyl alcohol (Fe3O4@PVA) nanocomposite film as a novel nanocatalyst was accomplished by in situ precipitation method. To enhance the catalysis activity, the surface modification of this nanocomposite was carried out by sulfonic acid. After the synthesis of this nanocomposite film, Fourier-transform infrared (FT-IR) spectroscopy, energy-dispersive X-ray (EDX) analysis, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) images, X-ray diffraction (XRD) pattern, N2 adsorption–desorption by Brunauer–Emmett–Teller (BET), thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM) were utilized to confirm the structure of the nanocomposite. The catalytic activity of Fe3O4@PVA was investigated by the synthesis of dihydropyrimidine derivatives from an aldehyde, ß-ketoester and urea or thiourea. This heterogeneous nanocatalyst can be easily separated by an external magnet and reused for several times without any significant loss of activity. Simple work-up, mild reaction conditions and easily recoverable catalyst are the advantageous of this nanocomposite film.