We report the frequency dependence of linear and nonlinear optical susceptibilities of H-silsesquioxanes of various cage sizes and conformations using the INDO/CI method coupled with the SOS method. The average dynamic refractive index of silsesquioxanes is found to decrease as the cage size increases, and its variation is very small for the different conformations of the same cage size at the same incident wavelength. The calculated second-order susceptibilities show that small cages have a larger magnitude which is comparable to that of crystalline alpha-quartz. It is suggested here that H-silsesquioxanes of a smaller cage size can be a good candidate materials for nonlinear optical applications having low absorption, wide transparency and adequate susceptibility in ultraviolet or vacuum ultraviolet region of the spectrum.