Graphene and graphene oxide attract rapidly growing interest as prospective building blocks for nanotechnology applications and composites. Recently, we showed that a small amount of graphene oxide produced significant templating effects on the structure of continuous carbon nanofibers (CNFs). However, the produced nanofibers had significant nonuniformities that could be detrimental to their mechanical properties. Controlled nanofabrication is critical for obtaining uniform, high-quality nanofibers with tunable diameters and properties. Here, we analyze the effects of graphene oxide type, concentration, and processing parameters on the morphology of continuous graphene oxide/polyacrylonitrile nanofibers produced by electrospinning. Four types of graphene oxides with different average nanoparticle sizes were examined, and the effects of electric field and polymer concentration on nanofiber diameters were analyzed. Good-quality nanofibers were produced with up to 2 wt % graphene oxide in polyacrylonitrile. Uniform nanofibers were obtained for solid content above 9 wt % in dimethylformamide (DMF). Composite nanofibers containing graphene oxide nanoparticles exhibited reduced diameters throughout the polyacrylonitrile concentration range before and after carbonization compared to nanofibers prepared from neat polymer. The obtained results open up a pathway for controlled nanofabrication of uniform CNFs with improved structure for a variety of structural and functional applications.