Abstract: Bulk polymers have a very low thermal conductivity of about 0.2 W/m·K. Polymer nanofibers prepared by electrospinning have a much higher thermal conductivity along the fiber axis. Graphene oxide (GO) was dispersed in a polyethylene oxide (PEO) solution and the resulting dispersion was electrospun into GO/PEO nanofibers. The fiber with 0.5 wt% GO had a thermal conductivity of 22.9 W/m·K, which is two-orders of magnitude higher than bulk PEO. Polarized FT-IR shows that the PEO fibers had different spectra in directions parallel and perpendicular to polarized IR. The intensity ratio of the peak at 1 099 cm^-1 between the parallel and perpendicular directions to the polarized IR was calculated. The curves of thermal conductivity and the intensity ratio against GO content are very similar, which suggests that molecular alignment is a key factor determining the thermal conductivity of the nanofibers. GO at low contents inhibits the movement of PEO chains because hydrogen bonds are formed between GO and a PEO chain during electrospinning and this improves the orientation degree of the PEO chain in the resulting GO/PEO nanofibers. With increasing GO content, the viscosity of the solution increases, which is unfavorable for the alignment of the PEO chain during electrospinning.