The objective of this research is to fabricate graphene nanopowder composites based on polydimethylsiloxane (PDMS) and to characterize the gauge factor of the graphene/PDMS composites for the use of strain sensors. The fabrication of graphene/PDMS composites can be accomplished by simple sonication and micro molding processes. We found that the measured gauge factors strongly depend on the concentration of graphene flakes in the composites. Obtained gauge factor of the graphene/PDMS composite strain sensor reached about 233 at a graphene concentration of 8.33 vol.%, which was measured within a strain range of 2%.