Five commercial poly(ethylene oxide)/poly(butylene oxide) (PEO/PBO) triblock copolymer surfactants were utilized as structure-directing agents to synthesize mesoporous silica under acidic conditions. The structures of these materials were characterized by using powder X-ray diffraction (XRD), nitrogen adsorption analysis, and transmission electron micrographs (TEM). The relationship between the pore sizes of silica mesostructures and hydrophobic block weight as well as block architecture of their block copolymer templates was discussed. From the comparison of the critical micelle concentration (CMC) values of these PEO-PBO copolymers and the resultant silica mesostructures, it is proposed that the CMC of block copolymers correlates to the final silica mesostructures and can be used as an important criterion for the rational design of ordered mesoporous materials especially when they are synthesized as precipitates from solutions. Such conclusions are useful to fabricate ordered and large pore mesoporous materials.