Abstract: 2D transition metal carbides and nitrides (MXenes) are a novel two-dimensional nanomaterial, which attracted extensive attention in the field of functional materials due to outstanding electrical, mechanical properties and abundant surface terminations. Therefore, it often has been used as building block for constructing macroscopic composites, such as MXene fibers, which are expected to be another structure-function integrated fiber after graphene fiber, and have widespread applications prospect in numerous fields, including smart textiles, sensing, energy, electromagnetic shielding, etc. However, the mechanical and electrical properties of MXene composite fibers are far lower than the intrinsic properties of MXene flakes. The main problems are that the existence of defects and voids in the MXene fiber caused by the wrinkling, disorder and weak interface interactions of MXene flakes during assembly, as well as the irregular shape of the fibers. In view of the existing problems as well as the future development direction, this review first introduces the fabrication approaches of MXene fiber. Then, we statement the mechanical and electrical properties of MXene composite fibers in detail, and discuss the strategies for improving the mechanical and electrical properties. Meanwhile, we outline the applications of MXene composite fibers by some instances. Finally, the existing scientific problems and challenges of MXene fiber are summarized, and the upcoming trends in MXene fiber are prospected, and some helpful viewpoint is provided for the research and application of MXene fiber in the future.