In this work, composites with different flake-like WS2 filler contents were prepared, using ethylene propylene diene monomer as matrix. The nonlinear electric conductivity of composites at 25, 50, and 80 °C was measured, and the mechanisms were analyzed. It is found that exfoliation of WS2 and testing temperature both have a direct influence on composites' electric conductivity. The inflection point and nonlinear coefficient of composites' nonlinear conductivity are also analyzed. The low WS2 content (4.31 vol. %) composite started to show nonlinear conductivity. Direct current dielectric breakdown strength was also measured. The thermal conductivity of composites was measured to verify the improvement of thermal conductivity. The obtained data show that the thermal conductivity of the composite can be increased to about 45% and 40% at 25 and 75 °C, respectively.