Four different types of silicon carbide fiber-reinforced silicon carbide matrix Composites (SiC/SiC CMCs) were fatigue tested in a simulated gas turbine engine hot section condition. The testing was performed in a unique atmospheric burner rig thermo-mechanical testing facility developed as a part of this study at the Air Force Institute of Technology (AFIT). Among the four SiC/SiC CMCs that differ by fiber type and processing method, the Sylramic- iBN fiber-reinforced and the prepreg melt-infiltration processed CMCs were shown to exhibit better resistance to the fatigue loading in the applied combustion environment. The effects of thermal stress, induced by the combustion heating applied on one side of each test specimen, were investigated using finite element modeling (FEM). The thermal stress added to the mechanically applied fatigue stress by a considerable amount, causing reduction in the overall stress at which sufficient cracking occurs and leading to failure by means of oxidative degradation. Optical and electron microscopic studies revealed that machined edges of the test specimen were susceptible to cracking and subsequently allowed oxidation to occur behind the tip of a crack that developed from the edges.