Polypropylene (PP) and styrene-ethylene-butylene-styrene triblock copolymer (SEBS) are blended at a ratio of 70/30 to serve as matrices, to which graphene nanosheets (GNs), the reinforcement, are then added to form PP/SEBS/GNs nanocomposites. A differential scanning calorimeter (DSC) test, tensile test, conductivity test, and electromagnetic interference shielding test are performed on the nanocomposites to examine the crystalline, mechanical, and electromagnetic properties. DSC results show that the content of GNs is proportional to the crystallization temperature of PP. The conductivity and electromagnetic inference shielding effectiveness (EMI SE) increase with an increase in the content of GNs, and can reach an optimal 0.244 S/m and 22 dB, respectively. The results of a tensile test show that an increasing content of GNs results in a decrease and then an increase in the tensile strength of the nanocomposites, until it reaches optimal tensile strength is 17.44 MPa.