Aggregation of nanofiller in polymer matrix is the key barrier to enhance the mechanical and thermal properties of polymer nanocomposites. Here, we report a novel vane mixer based on elongation flow processing, which is facial to achieve the homogeneous dispersion of functional graphene oxide sheets (FGs) in isotactic polypropylene (iPP). Scanning electron microscopy reveals that FGs in iPP matrix are fully exfoliated and uniformly dispersed. The crystallization behavior, mechanical properties and thermal stability of the nanocomposites with different FGs loadings are investigated by differential scanning calorimetry, dynamic thermomechanical analysis, and thermogravimetric analysis, respectively. The results illustrate that the mechanical and thermal stability of the iPP/FGs composites has enhancement obviously at low FGs loadings. POLYM. ENG. SCI., 59:830-837, 2019. (c) 2018 Society of Plastics Engineers