Statement of problem: marginal inaccuracy causes a space between restoration and prepared tooth, which accelerates cement dissolution, leading to secondary caries, pulpal lesions, postoperative sensitivity, periodontal disease and marginal discoloration. Marginal gap should be less than 120µm. Aim: to evaluate vertical marginal gap of PEEK (Bio-HPP) veneered with CAD/CAM composite veneer (HIPC) as compared to zirconia veneered with CAD-On lithium disilicate glass ceramic. And the effect of ageing on the gap of both restorations. Material and methods: 40 extracted molars were prepared, divided into two groups, control group (ZR) (n=20), teeth restored with IPS e.max ZirCAD copings veneered with IPS e.max CAD and intervention group (PEEK) (n=20), teeth restored with breCAM BioHPP copings veneered with BreCAM.HIPC. Each specimen was photographed using Leica S8 APO stereomicroscope under magnification 32X and image analysis was done. Measurements were taken twice before and after thermomechanical cycling. Results: PEEK group recorded higher gap mean values (49.88±7.97um) than zirconia (18.39±3.1um). This was significantly (p < 0.05) as confirmed by Mann-Whitney test, but all measurements were clinically acceptable. And Thermo-mechanical cycling had no effect of on both groups. Conclusion: PEEK veneered with composite can be used intra orally for single crown restorations.