The effects of surfactant and electron beam (EB) radiation treatment on the morphology and properties of polypropylene (PP)/expanded graphite (EG) composites were investigated. Surfactant treatment and sonication of EG before mixing with PP significantly influenced the morphologies of the composites, and the modification of EG with sodium dodecyl sulphate (SDS) had a strong negative influence on the electrical conductivities of these composites. The electrical percolation concentration is shifted from 5 to 6 wt% filler to about 10 wt% filler in the presence of SDS. The melting and crystallization temperatures of PP in the composites were not affected by surfactant or EB radiation treatment. There were small differences in PP crystallinity, depending on the type and combination of treatments. The filler particles acted as nucleating agents and the crystallization temperatures shifted to higher temperatures. The thermal stability of PP was significantly higher after irradiation, and improved even further for the samples containing EG, but the presence of EG had little influence on the thermal stabilities of the non-irradiated composites. For both non-irradiated and irradiated composites the maximum tensile stress and elongation at break values are lower than the neat matrix, while the tensile modulus increased significantly.