Directly, edge-propylene graphitic nanoplatelets (EPGnPs) are made easily using only solid graphite and propylene gas via the mechanical chemistry without additional reactions. The edge-propylene functionalization is confirmed using various analytical techniques (e.g. FT-IR, EA, and TEM). The hydrophobic characteristic and outstanding properties of the EPGnPs make it suitable as a new reinforcing additive for polyolefins such as polypropylene (PP). In result, the tensile strength, yield strength, and Young's modulus of EPGnP/PP_5 nanocomposites are enhanced 90.5, 90.8, and 249.5%, respectively and also show the higher thermal stability compared with raw PP due to its remarkable properties as well as the enhanced affinity between PP and propylene-functional groups of the EPGnPs. Based on experimental results, the graphitic nanoplatelets (GnPs) with various functional groups, especially, hydrophobicity, offer a number of advantages (e.g., excellent compatibility, economy, and mass-production) for use as a filler to expand the applications of polyolefin composites.