Polyacrylonitrile precursor fiber of a special grade for making carbon fibers was modified by stretching in the prestabilization stage to various extents. The effect of such stretching on tensile properties of the original precursor fiber, intermediate (oxidized) fiber, and resultant carbon fiber prepared through a continuous process was monitored. Improvements in tensile modulus of fibers at various stages were observed with increasing stretch ratios. However, no obvious enhancement of tensile strength of final carbon fibers was found.