Background: The marginal fit of dental restorations is a vital factor for long-term success. The veneering process of zirconia, which involves multiple firings at high temperatures, has shown to affect the marginal fit of zirconia cores. The aim of this study is to observe dimensional and marginal gap changes during veneer firing of zirconia frameworks sintered with different procedures. Methods: 30 Y-TZP ((inCoris ZI, Sirona, Bensheim, Germany) crown frameworks sintered with three different durations of 8 hours, 2 hours and 10 minutes. Occlusal and buccal dimensional measurements based on reference points measured with toolmaker’s microscope. Frameworks subjected to veneer firings without application of veneering material to observe the effect of firing process only. All dimensional and marginal gap measurements were repeated and after veneer firings. Data were analysed with one-way ANOVA and paired t test. Results: No significant differences observed between the sintering shrinkage of three groups. Marginal gaps decreased after veneer firings for all groups and the decrease was significant for 2 hour and 10-minute sintering groups (p <.05). The occlusal surface dimensional changes were negative which indicates shrinkage; again, buccal surface was positive which indicates enlargement. No significant differences between the three groups regarding surface dimensions were detected. Conclusions: For all three sintering groups, veneer firing caused distortion on zirconia structures in the form of shrinkage in occlusal surfaces and enlargement in buccal surfaces, whereas marginal gap values decreased after firing in all groups.