In this article, the overall mechanical properties of a short glass fiber-reinforced polyphenylene sulfide (PPS) composite were tested after oxidation at different temperatures (140, 160, 180, and 200°C), with a maximum oxidation time of approximately 5,300 h. In aspect of thermal aging process, the oxidation rates in 200 and 180°C are considerably harsher and faster than the case in 160 and 140°C, according to the concentration evolution of [C=O]. In aspect of mechanical properties, for virgin samples, due to an excellent fiber–matrix adhesion, no progressive damage is developed. Moreover, the fatigue results of aged samples show that the fatigue lifetime of PPS composites decreases more and more obviously with the oxidation time increasing while no significant loss of stiffness is observed. In addition, both monotonic and cyclic loadings are basically driven by the PPS matrix deformation. In the end, the relationship between fatigue lifetime and concentration of [CO] is built and discussed.