The principle aim of this investigation was to evaluate the influence of heat treatment on the fracture toughness and microstructure of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) substrate. Forty ceramic discs (10-mm x 4-mm) were prepared from YZ blocks using CAD/CAM technology, and divided into four groups according to frequency of the heat treatments, ten samples for each Group. Group I, no heat treatment (control group). Group II, are heat treated once corresponding to the first step of the veneering process. Group III, are heat treated five times to mimic the full veneering process. Group IV, Are heat treated seven times to represent the full veneering process plus two times entries for any correction reason. A hardness testing machine was used to measure the fracture toughness, and evaluation of the surface roughness was carried out using (ZYGO NewView 200 profilometer). Scanning electron microscopy (SEM) was employed to examine the surface of the ceramic specimens before and after heat treatment to observe morphology of the Y-TZP ceramic surfaces. X-ray diffractometer (Bruker Axs D8 Advance) analyses were conducted to determine the relative amount of the monoclinic phase of the disc specimens before and after heat treatment. Statistical significance among groups of population was analysed using one-way Anova and Pearson's correlation coefficient was used to determine significant correlation between fracture toughness and surface roughness. Statistical analysis of the mean fracture toughness (KIC) by ANOVA revealed that the difference between all groups was statistically not significant (P < 0.05). Also there was no statistically significant difference between mean surface roughness (Ra) of the four groups. There was no statistically significant correlation between fracture toughness and surface roughness in each group.