Abstract This paper deals with engineering geological properties of Qadis Khordak dam site in Northwest Afghanistan. This study is based on on-site and laboratory tests, surface discontinuity surveying, drilled borehole and permeability test of dam foundation. The engineering geological properties at the dam site were studied in order to evaluate geotechnical characteristics of rock masses at dam foundation, geotechnical properties of alluvium at dam axis, reservoir and borrow materials. The structural geological studies also carried out due to stability and safety of dam on their abutments reservoir and seismicity. Existence of a fault, high permeable zone at dam foundation and the thickness of alluvium at dam axis, are the most engineering geological issues that cause change on dam type selection. In the feasibility phase, the dam type was chosen as the concrete face rock-fill dam, because of state of engineering geological properties of dam site. However, in the design phase dam type has been changed as a rock-fill with a clay core.