Statement of Problem: Because commonly used obturating materials can not provide hermetic seal against saliva and microorganisms in the root canal system, thus it has been suggested that the use of intraorifice sealing of Gutta percha obturated root canals to prevent coronal micorleakage.      Purpose: The purpose of this study was to evaluate coronal micorleakage of four materials used as an intraorifice plug.Materials and Methods: After cleaning, shaping and conventional obturation of 86 extracted human single root canal and, a 3 millimeters of the gutta percha was removed from the coronal aspect of the root canal and replaced with one of the four filling materials: MTA, Glass Ionomer (GI), Coltozole and Amalgam. Microleakage was evaluated by using of staining penetration methods with Indian ink and after clearing of the specimens, the linear dye penetration was measured. The mean of linear dye penetration for each group was compared by the ANOVA and Post Hoc test.Results: The results showed that GI group had significantly the most leakage and the other experimental groups of Amalgam and Coltozole significantly sealed better. On the other hand, the MTA group had significantly the least leakage.Conclusion: The result of this study showed that although the three experimental materials (Amalgam, Coltozol and MTA) except GI were able to decrease the coronal microleakage, but none of them were able to prevent microlaeakge completely. So, use of orifice plug to reduce coronal microlaekage which is one of the important causes of failure in endodontic, seems to be useful.Key words: Coronal Leakage, Coronal Seal, Intraorifice Plug