The inversion of cyclohexane and cyclohexasilane has been studied by using ab initio molecular orbital theory at the MP2/6-31G* level. In total five stationary points (chair, twist, boat, C-5, and C-2) were characterized as minima or transition states. Frequencies of vibration were calculated for chair and twist conformers of C6H12 and chair of Si6H12. Our calculations, in agreement with an electron diffraction experiment, show that the energy differences for cyclohexasilane conformers are much smaller than for cyclohexane ones.