Interface roughness effects on quantum oscillations in ultrathin metal-oxide-semiconductor held transistors (MOSFETs) are investigated by numerical analysis. The interface roughness is described in terms of Gauss distribution. Quantum oscillations in ultrathin gate oxides are shown to be little damped by SiO2/Si interface roughness. The applied voltage shift at the extreme of quantum oscillations increases linearly with SiQ(2)/Si interface roughness increasing. This means that this shift may be used to obtain the information about the interface roughness as an inexpensive and simple tool.