The complete and dissociative ionizations of a 3,4,9,10-perylene-tetracarboxylic-dianhydride (C24H8O6, PTCDA) molecule in the gas phase have been studied, by using electron-impact mass spectrometry in an energy interval of 5–90 eV. The molecule is found to decay into the following fragment ions: the perylene core C20H8+ and its half C10H4+, as well as CO+, CO2+ , and O+ ions. The energy dependences of the cross-sections of the complete ionization of a PTCDA molecule and its fragment ions are analyzed. The energy of the complete ionization of a PTCDA molecule and the energies, at which its fragments appear, are determined. The temperature dependences of the formation of the most intensive fragment ions are measured, by using 80-eV electrons in a temperature interval of 320–500 K.