Structural change of methyltrimethoxysilane (MTMS), which can form sol-gel coating films via silsesquioxane, was investigated to elucidate the mechanism of coating at the early stage. Although films that can be used for sol-gel coating can be formed only after heating at about 100 degrees C for an hour, growth of nanoparticles was detected in the MTMS solutions at room temperature by static and dynamic light scattering. The existence and growth of nanoparticles were also confirmed by other measurements.