Purpose:Mechanical and surface characteristics of the zirconia dental ceramics may be adversely impacted by temperature changes during the veneering firing cycles. A potential synergistic failure could be caused by ageing when exposed to the oral environment and heat treatment. The current research aimed to determine the influence of heat treatment and in-vitro ageing on mechanical properties and surface roughness of cold isostatic pressed zirconia. Materials and Methods:15 bar shaped specimens with dimensions 28mm×4mm×2mm are milled from two types of partially sintered Y-TZP ceramic blanks (IPS e.max ZirCAD (IZ),ZENO Zr (WZ)). Out of 15 samples five are used as control (C group), five are heat treated (H group) and five are heat treated and subsequently aged (HA group). Flexural strength and shear bond strength are measured using universal testing machine and surface roughness is measured using proliferometer. Results:Heat treatment on the ivoclar and weiland samples led to an increase in surface roughness and a loss in mechanical properties (flexural strength and shear bond strength), although the differences are not statistically significant (p>0.05). Yet, the combined ageing and heat treatment created a synergistic effect on surface roughness and mechanical characteristics. (p<0.001). More variations were seen in the weiland samples. Conclusion:Firing and ageing processes may have an impact on zirconia ceramics clinical performance, which raises the risk of failure.