Abstract: Objective: To investigate the effect of thermocycling on the crystal structure of zirconia and measure the fracture resistance of zirconia cantilever fixed bridge with 0.7mm and 0.8mm in the posterior dentition. Methods: Two 10×15×1mm zirconia specimens (one served as control and another subjected to thermocycling, 100000 times, 5-55℃ ) were prepared. X-ray diffraction (XRD) was used to estimate the relative amount of monoclinic phase in each specimen. 12 zirconia cantilever fixed bridge frameworks were prepared by using CAD/CAM systems and divided into two groups (0.7mm and 0.8 mm, 6 in each group). All frameworks were cemented on the model using glass ionomer luting cement and then subjected to compressive test by using a Universal Testing Machine. The loads at fracture were recorded and one-way ANOVA was used to analyze the data. Results: No specimen exhibited the monoclinic phase before and after thermocycling．There was no significant difference in the fracture resistance between group 0.7mm (1262.08±100.57N) and group 0.8mm (1345.87±191.17N) (P>0.05). Conclusions: Thermocycling has no effect on the crystal structure of zirconia. The loads at fracture in both groups were more than the maximum human bite force (888N).