Abstract: In this study, the geological and geotechnical properties of the rock units along the derivation tunnelalignment were evaluated before construction of the Güledar dam. The main two formations crop out on the tunnelalignment and its vicinity. Güledar formation in Triassic aged consist of volcanic and metamorphic rocks with thePermian-Carboniferous limestone blocks. Sirkeli Formation which overlay Güledar Formation unconformably, consistof weakly consolidated and unconsolidated conglomerate, sandstone and siltstone with clay interclations. Q andGeomechanical RMR rock classifications were made by using the geotechnical parameters evaluated from the rock unitsof the tunnel aligment. The different support categories have been proposed for the rock units of the derivation tunnel ofthe Güledar dam.