The lateral-growth of Si-quantum dots (QDs) on linepatterned SiO2 from a thermal decomposition of pure monosilane has been systematically studied. We confirmed the Si-QDs diameter in the line direction of the line-patterns is rate-limited by the cohesive reaction of adsorbed Si precursors as same as OH-terminated SiO2 surface without the line patterns. It has been also found that, in the growth of Si-QDs in the line width direction, a surface migration of Si precursors adsorbed in-between lines could contribute, resulting in an elliptical growth.