Introduction: Using glass fiber post with resin materials which have mechanical properties close to those found in dentine offered a monoblock effect over restored teeth and thus more favorable strain and fracture resistance of remaining tooth structure. However, in flared canals the misfit of ready-made glass fiber post at coronal part leads to increased cement thickness at this area with more liability to voids incorporation and de-bonding risk. Different methods have been proposed to solve this problem, but still there is no definite data about the effect of each technique on mechanical properties of remaining tooth structure. Materials and Methods: a total number (n=32) of freshly extracted central incisor with nearly same length and diameter were used in this study and divided to four groups as the follow: group1 (control)(n=8) remain sound without any preparation or endodontic treatment, group2,3 and 4 received endodontic treatment and intra-radicular flared preparation with same criteria and restored as the follow: group2 (n=8) restored with radix fiber post, group3 (n=8) restored with relined radix fiber post, group4 (n=8) restored with EverStick fiber post. Coronal portion for all groups were then restored with nano-hybrid composite and all samples were then individually mounted on epoxy resin blocks and where loaded at 135ᵒ of the long axis using a computer controlled testing machine with a load cell of 5 KN. The specimens were statically loaded until fracture at a crosshead speed of 1 mm/min with the steel rod. Fracture patterns and failure mode of all samples were examined visually using magnifying lens to detect failure mode, favorable (repairable) or unfavorable (irreparable). Kruskal-Wallis test was used to study the different between tested groups. The significance level was set at P < 0.05. Statistical analysis was performed with IBM SPSS (SPSS Inc., IBM Corporation, NY, USA) Statistics Version 22 for Windows. Results: The fracture resistance testing revealed that intact teeth (control group) showed the highest mean fracture resistance value (462.89 ± 104.51 N). The Relined Radix fiber post group showed the highest fracture resistance values (392.03 ± 105.34 N), Radix fiber post group showed the lowest fracture resistance values (303.15 ± 95.39 N) and the EverStick Post showed (369.77 ± 107.4 N).The difference between the control and both Relined Radix and EverStick post groups were statistically insignificant (P > 0.05). However, the differences between the Radix post groups with all remaining groups were statistically significant (P ˂ 0.05). Mode of failure Assessment revealed that the intact teeth (control group) showed the highest percentage of favorable fractures (72.7%).Among the tested post types, the EverStick Post showed (63.63%) favorable fractures. While the Radix post group showed the lowest percentage of favorable fractures (27.27%) and The relined Radix post group showed (45.45%) favorable fractures. However, the difference between the groups was statistically insignificant (P > 0.05). Conclusion: 1. Endodontically treated maxillary anterior teeth with flared canals restored with individually formable glass fiber post or relined prefabricated fiber posts behaved in nearly the same manner under the subjected compressive load. 2. Relining ready-made glass fiber post or using individually formable glass fiber post in maxillary teeth with flared canals increase their fracture resistance. 3. Increased resin cement film thickness adversely affect fracture resistance and failure mode of teeth with flared canals. 4. The fracture value for all tested groups was higher than normal masticatory forces in anterior region.