A novel magnetically separable catalyst was prepared based on surface modification of Fe3O4 magnetic nanoparticle (MNPs) with polyethyleneimine (PEI) via covalent bonding. 3-(2,3-Epoxypropoxy)propyltrimethoxysilane (EPO) was used as cross linker to bond PEI on the surface of MNPs with permanent stability in contrast to PEI coating via electrostatic interactions. The synthesized catalyst was characterized by Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). The catalyst show high efficiency for one-pot synthesis of 2-amino-3-cyano-4H-pyran derivatives via multi-component reaction (MCR). This procedure offers the advantages of green reaction media, high yield, short reaction time, easy purification of the products and simple recovery and reuse of the catalyst by simple magnetic decantation without significant loss of catalytic activity. Covalently grafted polyethyleneimine on Fe3O4 magnetic nanoparticles as easily reusable catalyst for the synthesis of various 4H-pyrans. Display omitted •Polyethyleneimine modified Fe3O4 via covalent bonding as a novel water tolerance catalyst.•The catalyst showed high efficiency for one-pot synthesis of 2-amino-3-cyano-4H-pyrans in water.•Catalysts could be easily recovered and reused for several times without a significant loss in their catalytic activity.