Aim: This study aimed to evaluate the effect of thermal aging for 5000 and 10000 thermocycles on the flexural strength and flexural modulus of Polyether ketone ketone (PEKK), as well as the micro-strains induced on the supporting abutments by its use as double crown-retained removable partial dentures (RPDs) combined with zirconia primary copings in Kennedy Class I. Materials and Methods: The study was conducted using PEKK for fabrication of flexural strength specimens and double crown-retained RPD framework, and zirconia (ZrO2) for the construction of primary copings in maxillary Kennedy class I models. The study involved three groups according to time of testing (n=8): Group I included testing at 24 hours of storage, group II included testing after 5000 thermal cycles, and group III included testing after10000 thermal cycles. The flexural strength and flexural modulus were evaluated by a three-point loading test using a universal testing machine. The micro-strains were analyzed using the strain gauge technique. Results: Results of flexural strength revealed group (I) to have the highest value followed by group (II), then group (III). For flexural modulus, both groups (I) and (II) showed no significant difference between them, with significantly higher values than group (III). Regarding micro-strain results, group (III) revealed the highest value, followed by group (II), and then group (I). Conclusions: PEKK could be considered a polymeric material having a shock- absorbing property, but when subjected to thermal aging, it deforms and its flexural modulus and strength decrease, with more stress transferred to the supporting structures.