The hydrolysis of methyltrimethoxysilane (MTMS) and the polymerization of the silanols in acetone solutions have been investigated by infrared spectroscopy. The hydrolysis is monitored by using an absorption at 840 cm(-1) due to methoxy groups and the polymerization by using one at 900 cm(-1) due to silanol groups. When HNO3 is used as the hydrolysis catalyst, the rate of hydrolysis decreases upon adding aluminum acetylacetonate (Al(acac)(3)), and the polymerization proceeds to a high degree. In the absence of acid catalyst, Al(acac)(3) plays a catalytic role in the hydrolysis. These catalytic effects are discussed by assuming a transfer of proton between Al(acac)(3) and hydroxyl-containing species in the solutions.