Objective: Evaluating the flexural strength of different combinations of modified PEEK and 3-YTZP veneered restorations as well as the effect of aging on those combinations. Materials and Methods: Two core materials; partially sintered tetragonal monolithic zirconia and modified PEEK, and three veneering materials; lithium disilicate glass-ceramic, packable composite, and veneering porcelain were used. Total of sixty specimens were randomly divided into 3 groups (n=20). The specimens were constructed in the form of bilayered core/veneer disks of diameter12 mm and total thickness 1.5 mm. Half of the specimens of each group were tested for biaxial flexural strength using the piston-on-three-balls test. The other half of the specimens were subjected to artificial aging and then tested for biaxial flexural strength. Results: Two-way ANOVA showed there was a significant effect for the material of the bilayered restoration, aging, and the interaction between them on biaxial flexural strength. Unaged veneered Zirconia and Crea.lign veneered PEEK had significantly higher values (398.85±29.58) and (391.31±15.59) respectively than IPS e.maxCAD veneered PEEK (222.13±18.77). For the aged subgroups, veneered Zirconia (303.51±35.64) and Crea.lign veneered PEEK (277.10±13.37) also showed significantly higher values than IPS e.maxCAD veneered PEEK (198.10±6.57). For IPS e.max CAD veneered PEEK, there was no significant difference between unaged and aged sub-groups (p=0.100). However, for other materials, aging caused significant decrease in biaxial flexural strength values (p < 0.001). Conclusions: Both Crea.lign veneered PEEK and porcelain veneered 3-YTZP could be used with the same efficiency, regarding flexural strength, as bi-layered restorations. Aging has a negative effect on both materials' combinations