The thermal decomposition of Polyamide 66 (PA)/High-Density polyethylene (HDPE) blends at different compositions was studied. The results for activation energy show that when Polyamide 66 with HDPE blends are processed within the range of the compositions being studied, it is possible to obtain a material with similar thermodegradative properties than those corresponding to PA. These blends would represent an economically viable alternative, because a material would be obtained with low cost/property ratio. Of the presented results, it is inferred that the composition of 20% of HDPE is the one that presents greater thermal stability.