The concept of phase separation was coupled with electrospinning to induce polyacrylonitrile (PAN) and polystyrene (PS) bicomponent electrospun fibers that, upon removal of the phase-separated PS domains by solvent extraction, became nanoporous. Electrospinning of PAN (MW 150 kDa) with 5% w/w PS (Mw 250 kDa) at a 10 % w/w total concentration in N,N-dimethylformamide(DMF) produced fibers with stable morphology and average diameters from 1130 680 to 890 +/- 340 nm by FESEM. The nanoporous fibers made from a 95/5 w/w PAN/PS bicomponent precursor had internal pores of about 20 similar to 110 nanometers. Pore sizes of the porous PAN fibers were decreased to approximately similar to 25 nm after oxidation and carbonization thermal treatment because of fiber shrinkage during the thermal treatment. The fibers retained a high density of pores after the thermal treatment.