The objectives of this study were to compare the fracture strength of endocrown restorations fabricated with different preparation depth and various CAD/CAM ceramics, and to assess the fracture types. Endodontically treated 100 extracted human permanent maxillary centrals were divided into two preparation depth groups as short (S: 3-mm-deep) and long (L: 6-mm-deep), then five ceramic subgroups, namely: feldspathic-ceramic (Vita Mark II-VM2), lithium-disilicate glass-ceramic (IPS e.max CAD-E.max), resin-ceramic (LAVA Ultimate-LU), polymer infiltrated ceramic (Vita Enamic-VE) and monoblock zirconia (inCoris TZI-TZI) (n=10/subgroup). The endocrowns were fabricated by CAD/CAM and were cemented with resin cement (RelyX U200). The teeth were thermally cycled (5,000cycles) and fracture tests were performed at 45 angle to the teeth. The data were statistically analyzed (Kruskal-Wallis, Mann Whitney U), failure modes were evaluated with stereomicroscopy. Zirconia group provided the statistically highest fracture strength, but also exhibited non-repairable failures. Preparation depth has an effect on the fracture strength only for feldspathic ceramic.