To enhance mechanical properties through improvement of dispersion stability of carbon black (CB) in epoxy resins, fluorine functional groups were introduced on the CB surface by fluorination. The changes in the chemical properties and dispersion stabilities after fluorination were evaluated with different partial pressures of fluorine gas. The mechanical properties of the fluorinated CB/epoxy composites were evaluated by the test of tensile, impact strengths and creep behavior. The fluorinated CB/epoxy composites showed approximately 1.6 and 1.1 times enhancement in the tensile and impact strengths compared to that of neat epoxy, respectively. Moreover, when a constant load was applied at 323 K, the fluorinated CB/epoxy composites lasted longer and had smaller strain changes than those of the raw CB/epoxy composites. Thus, well-dispersed CB by fluorination in epoxy resins effectively transfers mechanical stress.