The formation mechanism of mesoporous molecular sieve materials MCM-41 in differ-ent synthetic systerns has been studied systendcally In the Na2O-(CTMA)2O-SiO2-H2O system,it is found that liquid-crystal templating mechanism should be that silica first forms silicated mi-celle with surfactant cation, then silica/CTMA+ micelle polylnerizes with each other forming thehexagonal mesophase. The experimental results in the TMAOH-SiO2-CTMABr-H2O system sup-ports the mechanism proposed for a surfactant-silica system from the lamellar to the hexagonalmesophase. Therefore, it is found that the formation mechanisrns of MCM-41 molecular sieves arenot the same under different synthetic conditions and in different synthetic systems.