In this work, chitosan/graphene oxide as a green bionanocomposite catalyst was synthesized and characterized by Fourier transform infrared spectroscopy (FT-IR) spectra, thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) analysis, atomic force microscopy (AFM) and scanning electron microscopy (SEM) images. Then, it was used as a nanocatalyst for the synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives by a one-pot three-component condensation reaction of benzaldehyde, 1,3-ketoesters and urea in excellent yields and short reaction times under solvent-free conditions. The reaction work-up was simple and the catalyst could easily be separated from the reaction mixture and reused in subsequent reactions. (C) 2016 Elsevier B.V. All rights reserved.