One of the main problems of dentists and endodontic for treatment of teeth in need for root canal therapy is the lack of perfect seal at the apical area to meet their requirements. The sealing properties of root canal filling materials is one of the most important factor that can influence apical seal. When filling the root canal system, the sealer plays an important role in reducing microleakage . A great variety of endodontic sealers are available commercially, and they are divided into groups according to their chemical composition such as zinc oxide eugenol sealers, epoxy resin sealers, and calcium hydroxide sealers. The aim of this research is to present an investigation regarding the in vitro comparison of apical leakage of RSA ( Roekoseal Automix ) and Roth 801 and AH26 sealers in lateral condensation technique using dye leakage method using new method for the leakage measurement.