Abstarct: Kordkooy county is located in the south east of Caspian sea and 29 km West of Gorgan. Drinking water of Kordkooy, Bandartorkman and Gomishan cities comes from the Kordkooy aquifer which experiences salination recently. There is a deep unconfined aquifer in the beginning of the plain, semi-confined and confined aquifers in in the middle of plain and some perched aquifer in the end of plain (near sea). Evaluation of isopotential maps shows that main groundwater flow occurs from the South East to North and North West. Measured Parameters in the field are electrical conductivity, pH and water temperature. Other parameters evaluated included Sodium, Potassium, Calcium, Magnesium, Bicarbonate, Chloride and Sulfate, which have been measured by Golestan Regional Water Authority laboratory. The results of electrical conductivity in the region show that, electrical conductivity has increased from the South and South East toward the North and North West (from heights to sea) which is relatively similar to the groundwater flow direction. Due to the drilling of deep wells and heavy pumping to supply drinking water for Kordkooy, Bandartorkman and Gomishan cities, water in this part is mixed with connate water and results in low quality water. At the end of the plain in the North West of region due to aquifer discharge, evaporation from water table, progressive of sea water and discharging ag, returned water into Ghareh-soo river, electrical conductivity of the aquifer is very high in this area. The long residence time of groundwater from recharge region to discharge region, low permeability and smooth topography of North and North East parts of region causes salt-fresh water boundary, advance to plain side and extracted water from the deep wells is believed to be the causes salinity of water in these parts.