Micrometer-sized monodispersed mesoporous silica spheres with adjustable particle diameter and adjustable pore structure were successfully prepared. Drops of a silica sol were injected by a microfluidic device into a heated oil bath where the droplets solidified during sedimentation. Drop size was varied by control of the rates of the oil flow past the silica sol injector. The silica sol was made by prehydrolysis of tetraethyl orthosilicate (TEOS) in an aqueous acidic solution using a triblock copolymer as the template. Acrylamide monomer was added in the sol after prehydrolysis to accelerate the solidification rate of drops in the oil bath. The amount of monomer was used to control the pore sizes in the silica particles. The effect of synthesis conditions on the morphology and pore structure of spheres was investigated. Silica spheres with different surface morphology and internal structure were obtained by changing the composition of sedimentation medium. Pore diameter and pore-size distribution can be adjusted effectively by controlling the concentration of silica source, acid or polymeric monomer in the aqueous phase. The prepared silica spheres have high-surface area (>550 m(2)/g), large pore volume (>1.1 cm(3)/g) and large amount of macropores. High-protein adsorption capacity (520 mg/g) was achieved in the adsorption experiments of bovine serum albumin (BSA). Pore structure of silica spheres was demonstrated to be a crucial factor to determine the protein adsorption capacity. (C) 2007 American Institute of Chemical Engineers.