Concrete dams which are constructed in narrow gorges on rock formations should be able to sustain the high pressure imposed from the water behind the dam. This pressure is transmitted to the rocks at the abutment and foundation through the concrete dam body. In double curvature concrete dams in which the pressure resulted from impounding is imposed to the abutments, choosing the dam site (from rock mechanics point of view) and recognizing rock properties at the abutments are of paramount importance. One of the most important parameters which have to be considered is the shear strength of contact surface between rocks and concrete in the abutments. In this paper that is resulted from a series of in-situ direct shear tests on four concrete blocks prepared on the rocks inside an excavated gallery at the abutments, the shear strength parameters and peak and residual strengths of the contact surface of rock-concrete at different applied normal stresses have been measured and reported. © ISRM International Symposium - 5th Asian Rock Mechanics Symposium 2008, ARMS 2008. All rights reserved.