Corona discharge treatment was applied to modify the surface of multi‐walled carbon nanotubes and carbon fibers. Successful functionalization was evaluated by ATR‐FTIR. Then, the neat and modified fillers were introduced into the epoxy matrix and nanocomposites containing different amounts of filler were obtained. The properties of neat epoxy and nanocomposites including morphology, thermal, mechanics, viscoelastic, and conductivity were evaluated. According to the results, it was found that the corona modification of fillers resulted in breaking of fillers agglomerates and improved their dispersion. The mechanical properties and thermal stability of modified samples were improved with respect to unmodified ones. To analyze the relationship between the interfacial interactions in the nanocomposites and tensile performance, a theoretical model germane to the mechanical behaviors of the nanocomposite was applied. It was found that strong interfacial interactions existed in the modified nanocomposites comparing the unmodified counterparts. Although the electrical conductivity of hybrid filler systems was increased, their tensile properties were reduced compared to CNTs/epoxy nanocomposites. POLYM. COMPOS., 39:E2298–E2304, 2018. © 2017 Society of Plastics Engineers