The oriented carbon nanotubes (CNTs)/polylactic acid (PLA) composite fibers was prepared by the modified electrospinning technology, and characterized by Raman, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and thermogravimetric (TG)/differential scanning calorimetric (DSC) analyses, respectively. Results showed that functionalized MWNTs have obvious orientation along the fiber axial in the interior of the electrospun PLA fibers, and improved the crystallization degree of PLA in the composite fibers due to the heterogeneous nucleation effect. The influences of polycaprolactone-functionalized multiwalled carbon nanotubes (MWNTs-PCL) on the performances of PLA fibers were studied. The crystallization region inside the MWNTsPCL/PLA composite fibers was enlarged by increasing the MWNTs-PCL content. As a result, enhanced crystallization temperature was obtained. Moreover, a small amount of MWNTs-PCL (0.5%) improved the thermal stability of PLA matrix, while excess MWNTs-PCL (3.0%) induced the decrease of the thermal stability of PLA resin due to the agglomeration of MWNTs-PCL. POLYM. COMPOS., 2012. (c) 2012 Society of Plastics Engineers