Continuous macroscopic aligned polyacrylonitrile (PAN) composite nanofiber sheets embedded with highly aligned PAN-grafted multiwalled carbon nanotubes (MWCNTs) have been prepared by electrospinning followed by hot-stretching. Homogeneous and highly aligned MWCNTs in the polymer matrix were obtained by hotstretching of the electrospun fibers, which led to a significant enhancement in the mechanical performance of the resulting composite nanofiber sheets. After hot-stretching, the tensile strength and modulus of an electrospun PAN nanofiber sheet (containing 2 wt% grafted MWCNTs) increased by 320.7% and 204.5%, respectively, compared with the values for the pristine PAN terpolymer. In addition we show, for the first time, that a Raman mapping method can be successfully employed to investigate the distribution and alignment of MWCNTs in nanofiber sheets.