To explain the mechanism of ionization of the α-pinene (C10H16), the VUV dissociative photoionization of C10H16 in an energy region of 7.9~15.5 eV has been investigated with a mass-spectrometer method photoionization mass spectroscopy using synchrotron radiation, the dissociation energies and the appearance energies for its fragment ions were predicted. The ionization energy of C10H16 and appearance energies for its fragment ions, C9H+13, C7H+10, C3H+6 and CH3+, were determined with photoionization efficiency spectroscopy. The total energies of C10H16 and its main photofragments were calculated using Gaussian 03 program. The ionization energy of C10H16, appearance potentials for its fragment ions, and the dissociation energies to produce them were predicted using high accuracy energy model. The dissociation energies of some possible dissociation channels to produce those fragment ions were determined based on comparison of determined appearance energies and energies predicted with the Gaussian-03 calculations. According to the results, the experimental dissociation energies were in reasonable agreement with the calculated dissociation energies of proposed photodissociation channels of C10H16.