Vacuum ultraviolet (VUV) photoionization and photodissociation of methylcyclohexane have been studied utilizing a reflectron time-of-flight mass spectrometer (RTOF-MS) with synchrotron radiation source.Photoionization efficiency curves (PIEs) of molecule ion C7H14+ and fragment ions C7H13+,C6H11+,C6H10+,C5H10+,C5H9+,C4Hs+,C4H7+,and C3H5+ were observed.The ionization energy of methylcyclohexane was measured to be (9.80±0.03) eV,and appearance energies of fragment ions were determined from the PIEs.Optimized structures of transitional states,intermediates and product ions were characterized at the B3LYP/6-31G(d) level and the energies were calculated using G3B3 method.Formation channels of dominating fragment ions were proposed.Intramolecular hydrogen migrations and carbon ring-opening were the foremost processes in fragmentation pathways of methylcyclohexane.