The aim of this study was to evaluate the effect of glazing on biaxial flexural strength of different zirconia core materials. Disc-shaped zirconia (ZirkonZahn, Cercon, Ceramill) specimens (15 mm x 1.15+/-0.02 mm) were prepared according to manufacturers' instructions. The specimens from each system were divided into 2 groups (N= 10): unglazed and glazed. Glaze liquid was applied on the entire surface of the specimens of the glazed group and fired according to manufacturers' instructions. Flexural strength test was performed in a universal testing machine (crosshead speed: 1 mm/min). Data were statistically analyzed using two-way ANOVA and Tukey's test (p= 0.05). The mean flexural strength values for unglazed ZirkonZahn specimens (1388+132 MPa) were significantly higher than those of unglazed Cercon (1104+124 MPa) and unglazed Ceramill (1172+127 MPa) specimens. The mean flexural strength of glazed specimens did not show any statistically significant difference. Glazing decreased the flexural strength results significantly for all systems (p< 0.05). Glazing decreased the flexural strength values for ZirkonZahn, Cercon and Ceramill specimens. Unglazed ZirkonZahn specimens revealed significantly higher mean flexural strength values than that ofunglazed and glazed zirconia materials tested in this study.