Abstract: In order to improve interfacial bonding between carbon fiber (CF) and polycarbonate (PC), sizing agents of water-borne polycarbonate (WPC) and water-borne polyurethane (WPU) containing carbon nanotubes (CNTs) were used to treat the CFs. CNTs were introduced onto the surfaces of the CFs by a sizing process. The effects of sizing agents and CNT content on the interfacial properties of the composites were investigated by two methods, a single fiber fragmentation test (SFFT) for the monofilament reinforced composite and a transverse tensile test for the directional bundle composite. The results show that WPU is more conducive to improving the interfacial bonding properties of CF/PC composites because of its film-forming property, and the addition of CNTs has a beneficial effect on the interfacial properties of the composites. CNTs can effectively prevent interfacial slip and therefore significantly improve the interfacial properties in the SFFT, while the improvement is not obvious in a transverse tensile test because the adhesion of sizing agents plays a leading role.