The flow behavior and the effect of the spinning conditions on the fiber properties and structure of the copolyesters, i.e., samples of copoly(p-hydroxybenzoate-bisphenol A terephthalate), were investigated. The experimental results indicated that the apparent viscosity was affected significantly by shear rate, melt temperature, and p-hydroxybenzoate unit content; and the copolyester melts exhibit highly shear thinning behavior. The fiber modulus increase with the increase in extrusion temperature and draw-down ratio, and the tensile properties could be improved when a high spin draw ratio was used. High birefringence, indicating the presence of mesophase, was observed on a hot-stage polarizing microscope. Scanning electron microscopy revealed that the fibers spun at relatively high temperature had a well-developed, highly oriented fibrillar structure. The fibers spun at low temperatures, however, were poorly oriented and nonfibrillar in character.