Objectives: the aim of this study was to compare fracture resistance of endodontically treated premolars restored with fiber reinforced post and different resin composite restorative materials. Materials and Methods: Eighty sound extracted premolar teeth were divided in to 3 groups; A (10 teeth kept sound as +ve control), B (10 teeth prepared only as –ve control), C (60 teeth divided into subgroup a as prepared and restored without post, and subgroup b as prepared and restored with prefabricated fiber-reinforced post (Glassix plus, Harald Nordin SA, Switzerland)). Each subgroup was divided into 3 divisions (n=10); 1 (coronal restoration with Tetric EvoCeram), 2 (coronal restoration with Tetric N-ceram), and 3 (coronal restoration with Tetric N-ceram Bulk-fill). All the teeth in group C were prepared for MOD cavities, root canal cleaned, shaped and obturated. All the teeth were subjected to thermo-mechanical aging and the universal testing machine by applying vertical compressive force at a crosshead speed of 0.5 mm/ min. All the data were collected to be subjected to quantitative statistical analysis. Results: Group A showed the highest fracture resistance values, and Group B showed the lowest values. Two-way ANOVA showed a significant difference among all groups. Conclusions: Bulk-fill resin composite restorations supported with prefabricated fiber-reinforced post improved fracture resistance of endodontically treated maxillary premolars.