In present work, nylon 6 (PA6) was grafted onto carbon fiber surface by means of anionic grafting to enhance the interfacial adhesion between carbon fiber and nylon 12. The effect of different grafting amount was studied by DTA, the tensile strength of PA6-CF/PA12 composites possessed a highest increase of 30.8% from 53.9 MPa to 70.5 MPa. The SEM of fracture surface of PA6-CF/PA12 composites demonstrated that the mechanical adhesion between carbon fiber and matrix PA12 was improved significantly. The experiments results indicate that it is an effective CF surface treatment to enhance the interfacial bonding with nylon 12 matrix by grafting nylon 6 to carbon fiber surface. Display omitted •Grafting PA6 onto carbon fiber surface is an effective method to enhance the mechanical strength.•The tensile strength possesses a highest increase of 30.8% from 53.9 MPa to 70.5 MPa.•The amount of nylon 6 lies on the amount of initiator and the reaction time. Nylon 6 (PA6) grafted onto carbon fiber (CF) after chemical oxidation treatment was in an attempt to reinforce the mechanical properties of carbon fiber composites. Scanning electronic microscopy (SEM), Fourier transform infrared analysis (FT-IR), X-ray photoelectron spectroscope (XPS) and thermogravimetric analysis (TG) were selected to characterize carbon fibers with different surface treated. Experimental results showed that PA6 was grafted uniformly on the fiber surface through the anionic polymerization. A large number of functional groups were introduced to the fiber surface and the surface roughness was increased. After grafting PA6 on the oxidized carbon fibers, it played an important role on improving the interfacial adhesion between the fibers and the matrix by improving PA12 wettability, increasing chemical bonding and mechanical interlocking. Compared with the desized CF composites, the tensile strength of PA6-CF/PA12 composites was increased by 30.8% from 53.9 MPa to 70.2 MPa. All results indicated that grafting PA6 onto carbon fiber surface was an effective method to enhance the mechanical strength of carbon fiber/nylon 12 composites.