Shorttitle: The development and maintenance of apical seal is desirable and considered to be a major prerequisite to improve the outcome of root canal treatment. Basically, two materials are used in combination for the root canals filling; a semisolid material (gutta-percha) and a sealing cement. Many types and brands of endodontic sealers are commercially available, but none of them fully satisfy all requirements and able to provide a fluid- tight seal. To address this problem the School of Dental Sciences, USM, has prepared a new experimental nano HA-filled epoxy resin based endodontic sealer using a simple and inexpensive technique. Nano-HA is biocompatible, reactive and has capability to adhere to the dentinal tubules. Moreover, it promotes apical healing and is able to produce hermatic apical seal. Different filling techniques based on heated or preheated gutta-percha have been introduced to enhance three-dimensional filling of the root canal. Little is known regarding the apical sealing ability of the new experimental nano-HA sealer when used with different obturation techniques.