INTRODUCTION: Polyetheretherketone (PEEK) can be used as a core material for fixed prosthodontics. However, information about the optimum veneer thickness of veneered PEEK restorations is still scarce. OBJECTIVES: To evaluate the effect of different composite veneer thickness on the optical properties of PEEK restorations. MATERIALS AND METHODS: Twenty four (n=24) PEEK (BioHPP granules) core disc-shape specimens of 15 mm diameter and 0.8 mm thickness were fabricated and veneered with composite resin (crea-lign, shade A3). The specimens were divided into three groups according to the veneering thickness: core/veneer thickness (mm) of 0.8/1.0, 0.8/1.5, and 0.8/2.0 for groups I, II, and III, respectively. The clinical spectrophotometer (VITA Easyshade) was used for color comparison with the reference color data of the selected shade stored in the device. Statistical analysis was performed with one-way analysis of variance (ANOVA) and student (Unpaired-sample) "t" test. RESULTS: The veneering thickness significantly influenced the ΔE values (p < 0.001). The mean color difference (ΔE) values for groups I, II and III were found to be 8.22(±0.41), 5.13(±0.43) and 3.23(±0.34), respectively. CONCLUSIONS: Color of PEEK restorations was significantly affected by the veneer thickness. The veneer thickness of 2.0 mm showed the best color match with perfect masking ability of the underling PEEK core(ΔE<3.3). In contrast, the veneer thickness of 1.0 and 1.5 mm showed a poor color match with poor masking ability of the underling PEEK core (ΔE>3.3).