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The effects of the addition of three different organosiloxanes, 3-aminopropyltrimethoxysilane (APTMS), 3-aminopropyltriethoxysilane (APTES) and 3-mercaptopropyltrimethoxysilane (MPTMS), on the phase behavior and the pore size of the surfactant-extracted materials have been investigated using powder XRD, TEM, Nitrogen adsorption/desorption isotherms and elemental analysis. The organosiloxanes were added to a typical synthesis, which results in a KIT-6 type in the absence of organosiloxanes. Their addition resulted in mesophase transformation or not, depending on the nature of functional groups of organosiloxanes. Increasing the content of APTMS or APTES in the silica sources not only led to the transformation of mesostructures from cubic bicontinuous Ia-3d to mixed mesostructure then towards two-dimensional (2-D) hexagonal p6mm and eventually to disordered structure, but also caused an increase of the pore size. However, the d spacing and the pore size of the cubic bicontinuous Ia-3d mesoporous solids can be decreased by addition of MPTMS between 0 and 2.5 mol% in the silica sources without a distinct decrease in the long-range order of the material. These results are discussed in terms of differences in the ability of the organosiloxanes to interact with the surfactant P123. The potential applications of these mesoporous materials are supports for the immobilization of enzymes, heavy metal sorbents, base catalysts, etc.