ABSTRACTThis study evaluated physical properties of the nanocomposites reinforced by used coffee grounds. Coffee grounds were ball‐milled and filtered in an effort to secure nanoparticles for the fabrication of polyvinyl alcohol (PVA)/coffee nanocomposites. We analyzed the particle size distribution of coffee particles and investigated mechanical and optical properties of the prepared nanocomposites. Carbon black (CB)‐filled nanocomposites were also prepared to understand the physical behavior of the nanocomposites reinforced with coffee grounds and to explore the possibility of replacing CBs with nanosized coffee grounds used as a composite filler. It was found that the tensile strength and Young's modulus of PVA/coffee grounds nanocomposites were significantly enhanced compared with those of the PVA/CB nanocomposites. In addition, morphological observation for the nanocomposites was carried out using scanning electron microscopy (SEM). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42043.