Calculations based on density functional theory (DFT) were performed on various structural isomers of methyl silsesquioxanes, [MeSiO3/2](n) where n = 4, 6, 8, 10, 12, 14, and 16, to study their structural and electronic properties. The calculated results find the stability of methyl silsesquioxanes, except [MeSiO3/2](4), against fragmentation and hydrolysis, and of one isomer of [MeSiO3/2](14) against hydrolysis. The deformation density plots show that chemical bonding in methyl silsesquioxanes is mainly determined by the building block unit, (MeSiO3/2) as also seen in hydridosilsesquioxanes (HSQ). However, unlike HSQ, the large cages of methyl silsesquioxanes do not develop a localized electronic state in the HOMO-LUMO gap.