Salinity is defined as the accumulation of water-soluble salt in soil and is one of the important factors affecting plant growth and the quality of ground water. The salt in soil is measured by electrical conductivity (EC), which increases with increasing salt amount. The first identification in the soil is performed in the laboratory EC analysis; Na variation percentage and pH determination are measured on field with adequate probes of portable pH meter, These measurements are conducted near surface soil layers about 30-40 cm of depth. However, if salinity of the deeper soil layers is to be measured, the soil samples must be collected from these soil layers. For this purpose, mechanical wells must be drilled until the desired depths. In this study, the salinity of the formations due to the intrusion of the sea water in the east of the Gulf of Izmit has been studied in situ by using geophysical (resistivity) method. The resistivity profiling survey enables the construction of resistivity maps that give a general plan view of the various alluvial deposits. Five sedimentary layers of different apparent resistivity were detected in the investigation area. These are gravely clayey sand (40-60 Omega m), gravely clayey silty sand (50 Omega m), clayey sandy gravel (100-110 Omega m), silty sandy clay (30 Omega m) and sandy silty clay (2 Omega m). The low resistivity values of sandy silty clay indicate high conductivity, which is related to the concentration of a conductive solute salty water intrusion from the Gulf of Izmit. The electrical resistivity soundings, coupled with the available drilling data, confirmed the presence of the sandy silty clay of low resistivity.