The purpose of the present study was to assess and compare between Biodentine and MTA as regards their biocompatibility using the intraossseous implantation method (Animal study) and as regards their sealing ability when used as a root-end filling materials using the dye penetration method (Leakage study).In the ˝Animal study ˝ part, white male Wistar Albino rats were used. All the experimental procedures were conducted in the animal house of the Faculty of Medicine, Cairo University (El Kaser El Eini). The surgical procedures were done under general anesthesia and longitudinal grooves parallel to the long axis of the shaft of tibia with a depth of 1 mm were made on the right and left tibias of each animal. The tested materials were loaded into sterile polyethylene catheter tubes, then they were implanted on the right tibia of each animal while empty polyethylene tubes were implanted on the left tibia of each rat to serve as a control. Thirty days after implantation, the animals were sacrificed and the implant sites were removed by gross dissection. The bone tissue specimens were prepared for histopathological examination and histomorphometric analysis.Results of the histopathological examination revealed the deposition of newly formed bone and the presence of variable sized fibrovascular marrow spaces with increase in the number of viable osteoblasts arranged at the periphery of bone trabeculae denoting active bone formation with mild chronic inflammatory cell infiltrate in both Biodentine and MTA groups. In the histomorphometric examination, results revealed increase in the formation of new bone in Biodentine and MTA groups.In the ˝leakage study ˝part, single rooted anterior teeth were selected, the teeth were prepared, obturated and then their roots were resected. Root- end cavities were prepared in all roots, and then teeth were divided into 2 equal groups according to the root-end filling materials; group І, filled with Biodentine and group ІІ, filled with MTA. The dye penetration test was carried out by immersing the roots into 50% silver nitrate solution then roots were sectioned longitudinally to measure their leakage extent using stereomicroscope. The results revealed that both Biodentine and MTA showed a low apical leakage.