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Hollow spheres of poly (1,4-phenylene-5-hydroxyisophthalamide) (PPHIA) which was an intractable aromatic polyamide were prepared by the reaction-induced phase separation during polymerization, and they are hopeful candidates as high-performance hollow spheres. In this study, porosity control of PPHIA hollow spheres was examined by optimizing polymerization conditions, focusing on polymerization temperature and time. Porosity became lower with smaller sphere size, and this tendency was more conspicuous at lower polymerization temperature. Skin layer gradually became thicker with polymerization owing to the accumulation of oligomers on both the outer surface and the inner surface of hollow spheres, resulting in the decrease in the porosity. The porosity of PPHIA hollow sphere could be controlled in the range from 4% to 16% by tuning polymerization temperature and time. [ABSTRACT FROM AUTHOR]