Highly porous polymeric hollow nanofibers were developed using a method based on coaxial electrospinning with inner silicon oil and outer polymer solutions. This method was verified by the fabrication of polymeric hollow fibers, whose diameter and wall thickness could be varied by controlling the coelectrospinning parameters, such as the dielectric constant of the solvents, concentration of the polymer solution, molecular weights of the polymers and viscosity of the inner silicon oil phase. The entire diameter and wall thickness of the hollow fibers could be varied from 5 to 15 mu m and 180 to 900 nm, respectively. Highly porous polymeric hollow nanofibers were fabricated by coaxial electrospinning with a highly volatile solvent. The interior surface was quite smooth without pores. Therefore, pore formation occurred at the outer surface of the hollow fibers due to rapid solvent evaporation because the jet only occurred between the surface of the polymer solution and air. The smooth interior and highly porous outer surface, circular cross-section and uniform size of the hollow polymer nanofibers are expected to have attractive applications in areas, such as catalysis, optoelectronics, nanofluidics, drug delivery or biosensorics.