Background: Root canal therapy is a sequence of treatments involving root canal cleaning, shaping, decontamination and obturation. Aim of the study: To compare efficacy of MTA and GIC as retrograde filling material. Materials and methods: The present study was conducted in the Department of Endodontics of the Dental institution.For the study, a total of 100 permanent maxillary central incisors without any caries or anatomical malformations were selected. The teeth were cleaned ultrasonically and were stored in normal saline.The teeth were randomly grouped into 2 groups, Group A and B, with 50 teeth in each group. The retrograde cavity of teeth in Group A were filled with MTA and in Group B were filled with GIC. The roots were exposed to an aqueous solution of a fluorescent dye for 24 hours and the dye penetration was studied using a microscope of a longitudinally section of each teeth. Results: The material used for retrograde filling in group A was MTA and in group B was GIC. Both the groups had 50 teeth each. We observed that mean dye leakage score was more in Group B as compared to Group B. Conclusion: Within the limitations of the present study, it can be concluded that MTA is efficacious in preventing microleakage when used as a retrograde cavity filling material as compared to GIC. Keywords: MTA, GIC, retrograde filling material, microleakage.