Abstract: Abstract： Objective An in vitro study was conducted to measure the fracture resistance of teeth restored with casting post and core with acid etched surfaces. Methods Thirty-two recently extracted single root first premolars were endodontically treated and randomly divided into four groups. Crown truncation was performed at cemento- enamal junction 1.5 mm coronally. All of the specimens received casting post and core and metal all crowns. In the testing groups, root canal walls were acid etched respectively for 10 s,30 s and 60 s，while root canal walls in the control group were not. Each specimen was cemented with zinc phosphate cement, embedded in acrylic resin, and tested in a universal material testing machine. Results The fracture loads of roots were （2.981±0.102） kN、（3.097±0.084） kN、（3.128±0.071） kN in testing groups and （2.699±0.445） kN in control group. There was statistical difference between all testing groups and control group (P<0.05). Conclusion Acid etching on root canal walls results in significantly higher fracture resistance of roots after post-core and crown restoration.