The morphology of the inner and the outer surfaces of polyetherimide (PEI) hollow fibers were studied by atomic force microscopy (AFM). The effect of the spinning conditions, namely, the bore liquid flow rate on the surface characteristics was investigated. Bore liquid flow rate was varied between 0.1 and 0.4 ml/min. The pore sizes at the outer and inner surfaces of the hollow fibers were affected by the bore liquid flow rates. Bore liquid flow rates also influenced the ultrafiltration performances of the hollow fiber membranes. The alignment of nodule aggregates to the direction of bore liquid Row was observed.