The pore sizes of SBA-15 materials have been reduced continuously by controlling the micelle properties of block copolymer EO 20 PO 70 EO 20 (P123) using the cationic surfactant cetyltrimethylammonium bromide (CTAB) as co-template, and the NH 4 F and KCl as inorganic additives. The resulting SBA-15 materials have been characterized by X-ray diffraction (XRD) patterns, N 2 physical sorption isotherms, and transmission electron microscopy (TEM). Experiments show that the pore sizes of SBA-15 decrease continuously from 8.49nm to 4.78nm with the increase of CTAB contents. However, the increase of CTAB contents results in lower structural ordering of the SBA-15 materials synthesized. The addition of F − dramatically improves the structural periodicity, but enlarges the pore sizes of the materials at the same time. In contrast, the introduction of KCl into the synthetic system can improve the structural ordering without evident effect on the pore sizes. It is suggested that the changes of micellar properties caused by the auxiliaries (CTAB, KCl, NH 4 F) should be responsible for the variation of the pore sizes of the resultant SBA-15.