'Caved-in' and spherical polypyrrole (PPy) capsules were successfully prepared by direct polymerization of pyrrole on polyelectrolyte hollow-capsule microreactors at different conditions. This microreactor was formed by alternate layer-by-layer (LbL) adsorption of chitosan (CS) and poly(sodium 4-styrenesulfonate) (PSS) on polystyrene (PS) colloidal particle and followed by removing the PS core with tetrahydrofuran (THF). The integrity and self-sustaining of the microreactor could be ensured through the chemical cross-linking of CS in multilayers with glutaraldehyde before the removing of PS. The direct polymerization of pyrrole on the microreactor, either polycations or polyanions at the outmost layer, can be achieved according to hydrogen bonding effect or electrostatic interaction. Participation of inorganic salts plays a significant role on morphology controllable of intact hollow polypyrrole capsules. (c) 2006 Elsevier Ltd. All rights reserved.