Rock testing for a dam project on rock foundation and for deign of underground facilities is very much essential for determination of strength and other index properties of the rock. It helps in getting basic knowledge of the stress state for engineering e.g in what direction and with what magnitude is the major principal stress acting and to have a specific and formal knowledge of the boundary conditions for stress analysis conducted in the design phase of large dam. Water and Power Development Authority (WAPDA) Pakistan has planned to build Diamer Basha Dam, a 272 m high RCC dam on river Indus for which the construction work is going to start soon. The dam would have two underground cavern type powerhouses on both sides of the dam. Laboratory as well as field tests have been carried out at the site for determination of the rock mass characteristics and strength. Rigid Plate Load and Flatjack tests were conducted at the site as a part of the geotechnical investigations. The paper summarizes the Geotechnical Investigations carried out so far at Diamer Basha Dam site and gives the details of rock mechanics tests.