The magnetic property of the LaMnO3−δ films was systematically investigated with the variation of the deposited oxygen pressure. The Curie temperature and the saturation magnetization of the films were found increased with the decrease of the oxygen pressure. We believe that the double exchange effect between Mn2+ and Mn3+ ions should be the origin of the ferromagnetism and the enhanced conductivity, where the Mn2+ ions are generated with the oxygen vacancies due to oxygen deficient, and the double-exchange interaction is enhanced with increasing the ratio of Mn2+/Mn3+. The results of the x-ray absorption spectroscopy support our conclusion as well.