Rock mass evaluation for the foundations of the Buyukyenice impervious central core rockfill dam to be constructed in the southwestern part of Balikesir, Turkey, was investigated. The geology under the foundation of the dam site is composed of silty clayey sandstone, silty sandstone, sandstone, tuff, and agglomerate tuff. The study involves three stages of field and laboratory studies and determination of bearing capacity of the foundation on which the dam body will be constructed. Detailed discontinuity surveys, geotechnical borehole drilling, Lugeon permeability tests, and sampling for index and some mechanical tests were performed in the field. Unit weight, apparent porosity, water absorption by weight, uniaxial compressive strength, and tensile strength tests were carried out on collected samples. The engineering classification of the rock masses at the dam site was evaluated by considering rock mass rating (RMR), rock mass quality (Q), rock mass index (RMi), and geological strength index (GSI). As a general conclusion, the rock mass at the dam site was divided into three classes from fair to very poor rock. Finally, the bearing capacity of the dam foundation rocks was computed for safe design.