The homogeneous carbon nanotubes (CNTs) directly grown on short cut carbon fibers (CFs) surface by chemical vapor deposition (CVD) using iron nanoparticles as catalyst. The iron nanoparticles were obtained by the reduction of magnetite particles using mixed nitrogen and hydrogen gas flow at 415 °C. Magnetite particles were prepared through a solvothermal reaction, where iron(III) acetylacetone as catalyst source and polylol as solvent. CNTs grown on CFs were used as reinforcement in epoxy (EP). The effects of density of CNTs grown on CFs (CNTs-CFs) and different mass fractions of CNTs-CFs in EP on the composites flexural strength were investigated. Results indicate that the reaction of iron(III) acetylacetone can synthesize magnetite particles of ca. 10 nm coated on CFs only in triethylene glycol (TREG) or polyethylene glycol 200 (PEG200). When CNTs grown on CFs surfaces at catalyst source concentration of 1.5 mmol/L, the flexural strength of CNTs-CF/EP composites with the addition of 0.8 wt% CNTs-CFs was improved by 28.1% to 102.5 MPa compared to that of pure EP. The homogeneous CNTs grown on CFs enhanced interfacial bonding are responsible for the improvement of composites flexural strength.