Abstract: A series of CMWNTs/PA66 composite fibers were melt-spun with the melt-blended PA66 and 0.1 wt%~ 3 wt% of carboxylic multi-walled carbon nanotubes chips. The effects of CMWNTs mass fraction on the morphology and mechanical properties of the composite fibers were characterized using SEM, DMA and a tensile strength tester etc. The results show that the CMWNTs are homogeneously dispersed throughout PA66 matrix. Both the T_g and mechanical properties of the composite fiber increase due to the addition of CMWNTs. When the mass fraction of CMWNTs is 0.5%, the storage modulus of CMWNTs/PA66 composite fiber is the highest, which is 5.5 times that of PA66 fiber. The glass transition temperature of the fiber is 27.6 ℃. When the mass fraction of CMWNTs is 0.3%, the initial modulus of CMWNTs/PA66 composite fiber is the highest with an increase of 101.4%. When the mass fraction of CMWNTs is 1%, the breaking strength is the largest with an increase of 48.8%.