Abstract: Multi-walled carbon nanotube (MWCNT)/Lyocell composite fibers were prepared and used as a precursor of carbon fibers to improve the mechanical properties of Lyocell-based carbon fibers. The structure and properties of the samples were investigated by wide angle XRD (WAXD), SEM, TGA and tensile tester. WAXD patterns showed that the composite precursor still had a cellulose II crystal structure. TGA curves showed that the thermal stability of the composite precursor was improved by the addition of the MWCNTs and the yield of the resulting carbon fibers could be increased. The SEM results showed that the surface and the cross-section of MWCNT/Lyocell composite fibers were smooth and round, which can meet the requirements of a carbon fiber precursor. MWCNTs were dispersed uniformly in the resulting carbon fibers. Compared with pure Lyocell-based carbon fibers, the tenacity and modulus of Lyocell-based composite carbon fibers containing 1% MWCNTs were increased by 70% and 116%, respectively.