To address the need for new smart hybrid materials, this paper presents graphene based nano composites which have piezoresistivity for strain sensor. Graphene/epoxy composites cast in a mold were fabricated to a composite strain sensor. The strain response of graphene/epoxy composites showed fairly symmetrical and reversible behavior, and the gauge factor obtained was about 11.4 within the range of 1000 micro-strain. The graphene/epoxy composite strain sensor showed much higher strain sensitivity than both carbon nanotubes (CNTs) composite strain sensors and the strain gauge made of high-quality graphene films. A contact area & resistance model of graphene was introduced to explain the higher piezoresistivity of graphene composites compared to CNTs composites. (C) 2010 Elsevier B. V. All rights reserved.