Materials and Methods: fifty extracted mandibular premolars were selected with completed, straight and single canal roots and free of caries or resorption or any previous treatment. The tooth crowns were removed and root length was adjusted to 16mm. Teeth were devided into five groups of 10 teeth each. Group I (control group) is non-instrumented teeth. Group II: canals were prepared with Mtwo rotary files and obtured by continouas wave compaction Group II: canals were prepared with Mtwo rotary and obtued by cold lateral condensation Group IV: canals were prepared with Reciprocblue files and obtured by continouas wave compaction. Group V: canals were prepared with Reciprocblue files and obtured by cold lateral condensation. The root were vertically loaded with testing machine (Testometric, USA) and the load when fracture was detected and recorded in newton. ANOVA test was used to determine differences regarding the fracture load of five groups, LSD test for dual comparison between groups was used. All stastical analysis was performed at 95% level of confidence. The results showed stastically significant differences in mean of fracture load between control group and other groups, also showed stastically significant differences between Reciprocblue and Mtwo groups, while did not show stastically significant differences between Continous Wave Compaction and Cold Lateral Condensation.