Copolyamic acid (coPAA) based on 4,4'-oxydianiline (ODA), p-phenylenediamine (PDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was synthesized in N,N-dimethylformamide (DMF). The preparation of continuous defect-free nanofibers from BPDA-PDA/ODA coPAA was achieved by electrospinning of its DMF solution. The average fiber diameter significantly increased from 385 to 590 nm on increasing the total polymer concentration of the spinning solutions from 5 to 7 wt%. The addition of dodecylethyldimethylammonium bromide (DEDAB) salt to the spinning solution resulted in the procurement of coPAA nanofibers with a much smaller (more than 3 times) average diameter. The coPAA imidization process was investigated through FTIR spectroscopy. The chemical composition and morphology of coPI nanofibers were assessed by X-ray photoelectron spectroscopy and scanning electron microscopy. Imidization under isothermal conditions proceeded faster in the first stage. Activation energies in the first and second imidization stages were similar when DEDAB had been added into the electrospinning solution. Cylindrical or crimped defect-free nanofibers of BPDA-PDA/ODA copolyimide (coPI) were obtained by the stepped thermal imidization of coPAA. The morphology of coPI nanofibers depends on the curing temperature. The crimped coPI nanofibers were most probably due to the relief of residual stress when the curing temperature was higher than the polymer glass transition temperature.