Abstract: Objective To compare the apical sealing effects of two kinds of root canal filling materials at different space-preparation time with dye penetration method. Methods 90 adults upper incisals were randomly divided into two groups which were 45 teeth, and prepared with back step method and obturated with lateral
condensation method with Cortisomol（A） and zinc-oxide-eugenol cement（B） as the root canal sealant. Then according to the post-space-preparation time, group A was randomly divided into 3 groups, which were A1, A2, A3, and
each group had 15 teeth. And then the same was done to group B, which were B1, B2, B3, and eachgroup had 15 teeth: Immediately（A1/B1）, two weeks later（A2/B2）, and four weeks later（A3/B3）. The different apical sealing
effects of the groups were evaluated with dye penetration method. Results There was significant difference on apical microleakage between group A and group B at every three space-preparation time（P<0.01）；and there was
significant difference at three different space-preparation time of group A（P<0.01）；but there was no difference in group B（P>0.05）. Conclusion The root canals were better sealed with Cortisomol than with zinc-oxide-eugenol
cement.

Key words: root canal obturation, post space preparation, microleakage