A microcalorimeter was used to investigate the formation mechanism of MCM-41 mesoporous silica. The obtained results show that. the formation processes of the sample contain three steps. On the basis of the calorimetric results, MCM-41 mesoporous silica was successfully synthesized under basic conditions at different experimental times, such as (l, 2, and 4) h, respectively. Associated with other analytical techniques, the formation mechanism of the produced silica is proposed. First; rodlike inorganic/surfactant complexes are formed which spontaneously pack into an ordered arrangement. Second, with the help of this new template, a new kind of pore structure is formed. Third, the interaction between the pore structures formed in steps 1 and 2 results in a new pore structure. This new pore structure is very similar to the structure formed in the first step. The present work proves that calorimetry can be used for investigations on the formation mechanism of materials.