The NW-SE trending Karacasu basin in the Aegean Extensional System cuts obliquely the Büyük Menderes graben. The Karacasu Basin was developed in the form of a half-graben with about 30 km long and about 10 km a width. This fault is called Karacasu Fault.The Pre-Neogene basement consists of schists and gneisses of the Menderes Massif. The Mio- Pliocene basin fill are represented by the conglomerates and sandstones along the basin margins, and mudstones and limestones at the basin center. This basin fill rest unconformably on the metamorphic basement, which is represented by the conglomerates and sandstones along the basin margins and mudstones and limestones at the basin center. The youngest unit is Quaternary units consists of coarse clastics. Based on direction, continuity and geometry of the Karacasu Fault is divided into two sub-segments as Çamköy and Yazır. Mountain front sinuosity (Smf), the ratio of valley floor width to valley height (Vf), stream length-gradient index (SL), asymmetry factor (AF), hypsometric integral (Hi) basin shape indices in the drainage areas and mountain fronts were calculated using DEM (12.5 m resolution) to determine the relative tectonic activity of the Karacasu Basin. By using the average of these calculated indices, the relative tectonic activity (Iat) index data point to was obtained. The relative tectonic activity of the segments with the obtained Iat index is divided into two classes. Iat index suggests very high relative tectonic activities for the NW tips of the both segments, while high tectonic activities was determined for the other parts of these segments. Based on findings on this study, the length of the segments and the ancient earthquakes in the region indicate the Karacasu Fault has a potential to produce earthquakes with M6 and or higher magnitudes earthquakes in the near future.