Objective To investigate the effects of post space preparation and post restoration on apical sealing ability. Methods 60 extracted mandibular premolars each with single canal were selected. All canals were prepared by manual ProTaper instrument using crown-down technique. The samples were the divided into 5 groups randomly. Group A: 20 samples, the immediate post space preparation group; group B: 20 samples, the delayed post space preparation group; group C: 10 samples, the intact group; group D: 5 samples, a positive control; group E: 5 samples, a negative control. There were two subsets in groups A and B which were restored by temporary materials（A1 and B1）or fiber post and cores（A2 and B2）. Indian ink dye method was used to measure the apical leakage in stereomicoscope. Results The mean length of dye penetration for group A1, A2, B1, B2 and C were （0.52±0.47）, （0.49±0.44）, （1.17±0.77）, （1.12±0.54）, and （0.23±0.40）mm, respectively. Positive group demonstrated maximum dye penetration, and negative group showed no dye penetration. There was no statistically significant difference between group A1, A2 and group C（P >0.05）. However, there were statistically significant differences between group B and group A, C （P
