Well-designed, monodispersed porous ZnO hollow microspheres with controlled hole-opening were successfully synthesized by a facile two-step solution route at low temperature. The hollow microspheres having average diameter of 3-4 mu m showed time-dependent hole-opening, i.e. 4-100% for 15-75 min. The hole-opening percentage increases linearly with time until complete opening. The ZnO hollow microspheres also exhibited a high surface area (34 m(2) g(-1)) a large pore volume (0.19 cm(2) g(-1)) and an average pore diameter of 3.8 nm. A plausible growth mechanism for the formation of ZnO hollow microspheres was also proposed.