The mesopores of mesoporous materials prepared with the anionic surfactant N-lauroyl-l-glutamic monosodium salt (AS) were enlarged by adding the cationic surfactant hexadecyltrimethylammonium bromide (CS) to the micelles of AS at pH 9. The ζ-potential of the micelles in the synthetic mixtures and the physical state of the assembled surfactants in the mesopores were examined by a light scattering spectrophotometer, 1H 13C CP-MAS NMR and DSC. The average pore diameters of the mesopores increased from 2.8nm to 6.2nm with increasing the content of CS. CS molecules inserted to the micelles composed of AS molecules, resulting in the enlargement of mesopores. However, the addition of too much CS interfered with the formation of the micelles. As a result, no mesoporous materials were produced when the ratio of CS to AS was above 80%.