Strain and pressure sensitive flexible piezoresistive sensors have been fabricated based on nanocomposites of graphene nanoplatelets (GNPs) and Polydimethylsiloxane (PDMS) elastomer. The strain detective sensors show positive piezoresistive characteristic under diverse levels of static strain up to 20% due to the flexibility and stretchability of PDMS elastomer. Tunable strain sensitivity of GNPs/PDMS piezoresistive sensors can be achieved by controlling GNPs incorporation into PDMS elastomer, which will be improved to 140 at 5 wt% GNPs concentration. In addition, pressure sensitive response, which exists when the pressure loading is less than threshold pressure, also can be observed in GNPs/PDMS piezoresistive sensors. The GNPs network-elastomer nanocomposite based pressure sensors show tunable piezoresistivity in the ranges of similar to 260 under increasingly higher GNPs concentrations. During the cyclic pressure loading, the pressure sensitive behavior of GNPs/PDMS nanocomposites manifests a superior dynamic correspondence with applied pressure while the resistance response can retain at a relatively high level under multiple loading-unloading cycles. Since the GNPs/PDMS piezoresistive sensors can not only respond to subtle bending but also distinguish them accurately for detecting the finger motions, it will make the GNPs/PDMS nanocomposite a good candidate for artificial skin and wearable sensor applications.