The formation of hydrous TiO2 (or TiO2 hydrates) by forced hydrolysis is a well-known sol-gel reaction. Self-assembly of nanosized primary TiO2 hydrates to monodisperse spheres has attracted numerous research interests for various applications. Recently the resultant hydrous TiO2 spheres (HTSs) have been demonstrated to be a versatile starting material for the facile and controllable synthesis of mesoporous anatase spheres (MASs) with large surface area and well-organized nanocrystallites. This mini review firstly summarizes the chemical pathways to the synthesis of HTSs. Key parameters toward size-controllable synthesis are discussed, and the structural properties of various HTSs are compared. Then the hydro/solvothermal transformation of HTSs to MASs with selective solid or hollow inner structures is described, along with the underlying mechanism. Finally, recent advancements of MASs for environmental photocatalysis and dye-sensitized solar cell applications are briefly highlighted. (C) 2013 Elsevier B.V. All rights reserved.