Composite nanofiber sheets of well-aligned polyacrylonitrile nanofibers (PAN) containing multiwall carbon nanotubes (MWCNTs) were prepared by electrospinning a MWCNT-suspended Solution of PAN in dimethyl formamide using a moving collector. Scanning electron microscopy, atomic force microscopy, transmission electron microscopy (TEM), IR spectroscopy, Raman spectroscopy, X-ray scattering, and the Instron test were used to characterize the nanofiber sheets. TEM observation showed the MWCNTs were parallel and oriented along the axes of the nanofibers. The mechanical properties of the composite nanofibers were reinforced by MWCNT fillers. Carbonization processes showed that a higher concentration of MWCNTs effectively resisted heat shrinkage of the composite nanofiber sheet.