Polyaniline (PANI) hollow microspheres constructed with their own nanofibers were prepared by inversed microemulsion polymerization associated with a template-free method in the presence of beta-naphthalene sulfonic acid (beta-NSA) as the dopant. The hollow microspheres were 4.0-6.0 mu m in outer diameter and 150-250 nm in shell thickness; they consisted of the nanofibers (20-30 rim in diameter and 150-250 nm in length). We propose that the coordination effect of the reversed emulsion and the dopant or dopant/aniline micelle might have been a driving force in the formation of the special microstructures/nanostructures, where the reversed microemulsion acted as a soft template in the formation of the microspheres and where NSA or the aniline/NSA micelle was regarded as a soft template in the fort-nation of the nanofibers. The molar ratio of water to the aniline/NSA salt and ultrasonic irradiation were critical in the control of the formation yield and the diameter of the uniform microspheres. (c) 2006 Wiley Periodicals, Inc.