Abstract: In this study, combined geophysical methods were performed to determine layered seawater-freshwater interface which is under natural conditions through a semipervious layer in a coastal alluvium of Gokceada-Turkey. The surveyed area named Kalekoy is located in the northeastern part of Gokceada. Electrical resistivity tomography technique with using dipole-dipole electrode configuration was performed over two profiles. The interpretation of the two-dimensional inversion of the acquired resistivity data delineated the seawater-freshwater interface successfully. Additionally to the resistivity data, two-dimensional seismic refraction tomography survey was also conducted to characterize the alluvium properties in terms of saturation conditions. It was determined that the soil is characterized with unconsolidated sediments. This study yielded useful information about the geometry of seawater body under the freshwater. The interface was determined at the depth of 7-8 m approximately and presents an undulated surface. Moreover, it was observed that seawater intruded far distant than the length of the survey area (>150 m).