The commonly used materials in endodontic treatment lack the ability to prevent microleakage, which can lead to failure of the treatment. This study aimed to evaluate the effectiveness of adding Coltosol plug in preventing coronal microleakage in endodontically treated teeth using the in vitro dye penetration method. Ten single canal plastic teeth were prepared and obturated using the SG-endodontic technique. The teeth were randomly divided into two groups, with and without Coltosol plug, and dye penetration was measured at 6 and up to 72 hours. No difference in leakage was observed after 6 and 72 hours. Specimens with a plug of Coltosol showed similar dye penetration compared to the ones with only Gutta-percha and sealer.