Perforation of the root canal system is the second largest cause of root canal failure. Failure to seal the perforation defect permits rapid break- down of the periodontium and eventual loss of tooth. Hence sealing the defect is of paramount importance. Although root perforations may be repaired surgically, furcation perforations are usually inaccessible by surgical approach, especially if the defect is situated lingually, in a mandibular molar. Moreover, surgical procedure will often lead to loss of attachment, chronic pocket formation, and peri-odontal furcation involvement. Perforations have been treated using a non-surgical intracoronal procedure of placement of a repair material into the defect. Amalgam and lightcured Glass ionomer cement are the most commonly used repair materials though both of them show extrusion into the furcation area. An in vitro study was carried out to evaluate the ability of calcium sulphate barrier to control the extrusion of repair material into the furcation area and to study the effect of these barriers on sealing ability of repair material. It was found that calcium sulphate provided a successful barrier against over extension of repair material, though the sealing ability of amalgam and Glass ionomer cement was significantly reduced by it. Glass ionomer cement over calcium sulphate was considered a better combination if the amount of extrusion and sealing ability of the materials are considered.