Elastomer nanocomposites reinforced with carbon nanofiber (CNF) decorated with metal nanoparticles exhibit excellent thermal, mechanical, and magnetic properties with low volume fraction of the reinforcement. Generally, metal nanoparticles are used to modify the surface of CNF, to improve their dispersion and contact resistance in the polymer matrix. In this study, Fe 2 O 3 metal nanoparticles were decorated on CNF by electrostatic attraction via a green and facile solution-based method. Interestingly, the CNF decorated with Fe 2 O 3 (CNF-Fe 2 O 3 )/elastomer improved both the tensile strength and the fatigue property of plain CNF/elastomer by as much as 57.2% and 27.2%, respectively. Moreover, the CNF-Fe 2 O 3 /elastomer exhibited superior thermal conductivity, a twofold enhancement compared with carbon fibers. The elastomer nanocomposites consisting of CNF-Fe 2 O 3 also exhibited enhanced magnetic properties due to synergies between the Fe 2 O 3 nanoparticles and the CNF. The elastomer nanocomposites prepared with CNF-Fe 2 O 3 will open significant new opportunities for preparing advanced elastomer nanocomposites for future engineering applications.