The Edremit Gulf is situated on the upper Miocene transtensional basin in the Western Anatolia and formed by the interaction between the North Anatolian Fault (NAF) and the N-S extensional tectonic regime of the Aegean domain. Our study is aimed to investigate the structural effects of these tectonic forces in the Gulf. Thus, approximately 300km. seismic data were collected within the Gulf area using the high-resolution seismic reflection method. The results indicated that the interpretation of the data, an E-W oriented, strikeslip fault system (Edremit Bay Fault-EBF) was identified in the Gulf as a possible continuation of the Havran-Balıkesir Fault Zone which can be followed on land. Likewise, a second strike-slip fault system (Edremit-Lesbos Fault; ELF) was observed which crosses the Gulf towards Lesbos Island in the NE-SW direction. This system was interpreted as the possible continuation of the Yenice-Gönen Fault Zone which is thought to be the branch of the North Anatolian Fault.