Morphology control of poly(2-oxy-6-naphthoyl) (PON) was examined by using reaction-induced crystallization of oligomers during direct polycondensation of 2-hydroxy-6-naphthoic acid with p-toluenesulfonyl chloride and NN-dimethylformamide in pyridine. PON particles were obtained of which the diameter was in the range of 8.0-8.3 mu m. The particles were comprised of many lamellae and exhibited spherulitic morphology. They possessed high crystallinity evaluated from wide-angle X-ray scattering (WAXS). Formation mechanism of the particles was clarified from the results of morphology observation, yield, density and WAXS. When the number average degree of polymerization of the oligomers exceeded a critical value of ca. 4-5, they were precipitated to form lamellae. The lamellae grew to spherulites through screw dislocation with continuous precipitation of the oligomer from the solution. Finally, further polymerization occurred gradually in the precipitates. Copyright (c) 2005 John Wiley & Sons, Ltd.