The effect of PCBM on the thermal stability of three conjugated polymers widely used in organic electronic applications, namely P3HT, MDMO-PPV and PFO, was studied under induced thermal stress (thermolysis and thermo-oxidation) using both dynamic and isothermal thermogravimetric analysis. The aim of this study was to test the potential anti-oxidant effect of PCBM on conjugated polymer:PCBM blends at high temperatures relevant to polymer melt techniques, and to evaluate the corresponding time and temperature windows of processability. Under thermolysis conditions (N2 atmosphere), most of the blends are less stable than the pure compounds. However, all the blends considered showed increased thermo-oxidation stability (air atmosphere) in comparison to the pure conjugated polymers. These results show that PCBM can be used as an efficient anti-oxidant to increase the time and temperature windows of processability of conjugated polymers at high temperatures under a normal air atmosphere.