Decane has been used as swelling agent to enlarge the pore size of pure silica MCM-41 materials. The synthesis conditions such as the swelling agent/surfactant molar ratio, the adding sequence of swelling agent, etc., have been studied. The role of decane and the effect of crystallization time and temperature on the synthesis have also been discussed. Final compounds were intensively characterized by several techniques (XRD diffraction, SEM, TEM, and nitrogen adsorption-desorption analysis). The present work shows that decane is an effective expander to enlarge the pore size of mesoporous materials. Two possible mechanisms have been proposed to describe the swelling effect of decane molecules. The synthesis of mesoporous materials can be explained by different steps, which have been observed in the synthesis course of zeolites.