In this work, we studied the effects of multi-walled carbon nanotubes (MWNTs) concentration and pH on the morphologies, microstructures and mechanical properties of the resultant poly (vinyl alcohol) (PVA)/MWNT composite nanofibers prepared by electrospinning technique. The PVA solution dissolved in distilled water was blended with various acid-treated MWNTs concentrations ranging from 1.0 to 3.0 wt%, and then electrospun to produce PVA/acid-treated MWNT composite nanofibers. The PVA/acid-treated MWNT nanofibers were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD), and tensile testing. SEM analysis demonstrated that the PVA/MWNT nanofibers with acid-treated MWNTs of 1.0 wt% gave rather smaller diameter and narrower distribution, suggesting well-distribution of the MWNTs onto the PVA nanofiber matrix, as also confirmed by TEM analysis. In addition, it was observed that the PVA/acid-treated MWNT (MWNT concentration similar to 1.0 wt%) nanofibers at higher pH gave lower diameter than those at lower pH, due to a decreased molecular interaction between PVA and acid-treated CNTs, and thereby results in a decreased viscosity and their diameters. Moreover, the resultant nanofibers at lower pH have better mechanical properties than those at higher pH. (C) 2012 Elsevier B.V. All rights reserved.