Abstract: Carboxylated carbon nanotube-filled polymethylmethacrylate (CNT/PMMA) ultra-long composite nanofibers were prepared by electrospinning of in-situ polymerized CNT/PMMA bulk composites under shear flow in a quartz capillary tube. They were characterized by SEM, TEM and FT-IR. The degree of orientation of the CNTs in the nanofibers was investigated by polarized Raman spectroscopy. The force imposed on CNTs by the poiseuille flow was analyzed. Results indicate that the nanofibers are smooth with a diameter of around 100 nm and a uninterrupted length of several meters. The CNTs in them are well dispersed and highly aligned parallel to the fiber axis. Chemical bonding between the carboxylated CNTs and PMMA is found. The electrical conductivity of the nanofibers is increased by 10 orders of magnitude by adding 8 mass% of CNTs. The alignment of CNTs in the nanofbers was induced by the shear force of PMMA on CNTs during the electrospinning.