Spheres of mesoporous silica were prepared in aerosol phase of acidic TEOS sols having structure-directing agents (SDA) such as cetyltrimethylammonium bromide (CTAB) and Pluronic P-123. Their structural characteristics were investigated by systematically varying the chemical and thermal conditions of preparation with TEM, FT-IR, BET and SAXS. Both SDAs produced well-assembled 2-D hexagonal structures. Alcoholic solvent left better order with smaller d values than aqueous one. The upper SDA concentration for mesoporosity was much lower in the former than the latter. To get the highest order, it was important to obtain the complete self-assembly of SDA molecules without any deterioration prior to calcination. Well self-assembled mesophase appeared for the product spray dried at 100 ℃ and subsequently calcined at 400 ℃. One-hour calcination yielded the best order. The number of domains increased with the calcination period up to 5 hrs and then decreased in further extended period. CTAB was bonded to silica surface to preserve the affinity to OH after it disappeared while P123 was not the case.