Objective To evaluate the effect of different root canal irrigants on smear layer removal and dentinal tubule opening of root canal surfaces after post space preparation. Methods Thirty maxillary anteriors were endodontically treated. After post space preparation, the teeth were assigned to three groups with ten teeth each: group A, B, C. 3% H2O2, 15% ethylenediamine tetraacetic acid（EDTA）, 15% EDTA and 3% NaClO were used as irrigant of group A, B, C. After post space irrigation, eight teeth of each group were examined under scanning electron microscope （SEM） for smear layer removal and dentinal tubule opening. The left two specimens were restored with fiber posts and prepared for evaluation of resin tag formation. Results The cleansing effectiveness of group A, B and C was respectively 3.89±0.36, 1.77±0.30, 1.25±0.21. The dentinal tubule opening of group A, B and C was respectively （2.53± 0.19）, （3.11±0.23）, （3.83±0.52）μm. The cleansing effectiveness and dentinal tubule opening of root canal surfaces were significantly affected by different root canal irrigants（P
