Graphene-based polymer nanocomposites have received much attention in the field of new hybrid materials, and in the enhancement of properties and diversification of applications. In this work, reduced graphene (rGO) and silver nanoparticles (AgNPs) were cooperated with poly(lactic acid) (PLA) (a semi-crystalline and brittle polymer) to improve mechanical strength and conductivity of the composites. The effect of various concentrations of stearic acid (SA-a precursor) on the formation of silver nanoparticles on graphene and its composite with PLA was studied for the first time. The rGO and AgNPs were first prepared using SA to enhance the AgNPs formation and improve surface wetting of rGO/AgNPs in PLA. The XPS atomic concentration of AgNPs in rGO-Ag-SA1 composite (1:1 mass ratio of SA: graphene oxide) was 5.77%, while, 2.55% in the rGO-Ag composite without SA. This enhancement is due to substitution of AgNPs onto the epoxy and hydroxyl groups on the graphene sheet. In addition, tensile strength of PLA-rGO-AgNPs-SA was higher than neat PLA when AgNPs and SA were added into the composites, especially the composite of PLA-rGO-Ag-SA1 which showed the highest strength increase of 47%. The volume resistivity of PLA-rGO-Ag-SA1 film was also two times lower than PLA-rGO-Ag; thus, this graphene-based composite of PLA-rGO-Ag showed a significant advantage for applications where antistatic properties are required along with an improvement of PLA's tensile strength.