Bimodal mesoporous anatase-phase TiO2 hollow microspheres are one-pot fabricated by hydrothermal treatment of acidic Ti(SO4)(2) solution with NH4F. Fluoride not only induces the outward hollowing of the spherical TiO2 aggregates, but also promotes the crystallization of primary anatase TiO2 nanocrystals, resulting in enlarged crystallite sizes and decreased specific surface areas. The hierarchical mesopores exhibit peak intra-aggregated mesopore sizes of 3-10 nm and peak interaggregated mesopore sizes of 30-50 nm, depending on the specific molar ratio of fluoride to titanium (R). The pore volume increases in parallel with the average pore size with increasing R until the collapse of interaggregated pores at R = 2. The photocatalytic efficiency in decomposition of gaseous acetone by as-obtained hollow TiO2 microspheres generally exceeds that by Degussa P25 when R is <2. The influence of fluoride on photoactivity are discussed in terms of phase structures and pore structures. (C) 2007 Elsevier Inc. All rights reserved.