MCM-41 is one of the groups of mesoporous materials that have wide applications as adsorbents, ion exchangers and catalyst supports. In this work spherical and rod-like MCM-41s were synthesized in homogeneous and heterogeneous reaction media, respectively. For synthesis of these materials the cationic surfactant cetyltrimethylammonium bromide (CTMABr) was used as template and tetraethylorthosilicate (TEOS) was used as the silica source. The polymerization process of the silica source was performed in basic and acidic media using ammonia or HCl as catalysts. BET (Brunauer-Emmett-Teller), FTIR, X-Ray diffraction and scanning electron microscopy analysis confirmed the structures of these synthesized materials. Finally a mechanism was proposed for the formation of these structures.