This paper discusses the results of the site investigations and rock mechanics studies carried out at the proposed Shahid dam site. Engineering geological properties of rock masses, such as permeability along the dam axis, discontinuities, strength, and stability of abutments, were investigated in order to determine probable problems prior to constructions.Shahid Dam is an earth fill dam with the clay core. The dam on the Marbor river, is located about 110 km of south of Semirom city in the Isfahan Province, Iran. The dam and its associated earth structures are mainly founded on alluvium and limestone in the High Zagros zone. Quaternary alluvium at the dam site has a thickness of about 20 m and overlies the Surmeh, Gadvan and breccia formations, comprises the Jurassic, Cretaceous and Post-Cretaceous rocks of the Zagros Mountains. Studies were carried out both at the field and the laboratory. Field studies include engineering geological mapping, intensive discontinuity surveying, kinematical analyses, drilling, Lugeon and Lofran permeability tests, and sampling for laboratory testing. Rock mass classifications, strength characteristics, and constants of rock masses wereexpressed by using Hoek-Brown empirical failure criteria, RMR, GSI, and Q values. The results of the investigations indicate that the foundation rocks are suitable for designing the proposed Shahid dam, and the rocks exposed in the right bank are of higher quality rock masses when compared to those in the left bank.