Aimof the study: The purpose of current study was to evaluate and compare the effect of different connector designs on the compressive strength of posterior inlay-retained fixed dental prostheses made from two different ceramic systems. Materials and Methods: Twenty-eight inlay retained fixed partial denture (IRFPDs) were used to replace missing lower right first molar. According to the IRFPDs material (lithium disilicate ceramic and Zirconia), the specimens were divided into two main groups A and B (n=14). These groups were further subdivided into 2 sub-groups 1&2 (n=7) according to the connector designs used (round and sharp). The IRFPDs were manufactured using the hot press and CAD-CAM techniques respectively. All specimens were cemented using self-adhesive resin cement. Each specimen was placed on the test device, and compressive force was applied till the failure occurred. All the results obtained were statistically analyzed by two way ANOVA test and student t test (level of significance p < 0.05). Results: Revealed that the highest mean value of compressive strength was for round connector with zirconia IRFPDs. While the lowest value was for sharp connector with lithium disilicate IRFPDs. Conclusions:Within the limitations of this in-Vitro study the following conclusion could be obtained; zirconia demonstrated high compressive strength than lithium disilicate. Despite the lithium disilicate possessed the lowest compressive strength values for both types of connector design. However these values were greater than the average occlusal force recorded in several studies.