Polypropylene (PP) based nanocomposites with graphitic carbon nitride nanosheets (CNNSs) exfoliated from g‐C3N4 (CN) were fabricated via melt compounding. The detailed structure and morphology of the CNNSs were examined using X‐ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscope (TEM), and atomic force microscopy (AFM) measurements. The effects of CNNSs on the crystalline morphology, oxygen vapor permeability, and mechanical properties of PP based nanocomposites were carefully evaluated. The CNNS not only increased the crystallization peak temperature and crystallinity, but also enhanced gas barrier properties and tensile strength of the PP nanocomposites. For PP/CNNS‐2 nanocomposites, the tensile strength was increased by 10.7%, and oxygen permeability coefficients decreased by 64.5% compared to pure PP. Therefore, PP/CNNS nanocomposite could be a potential candidate for packing application.