Gumuldur region is one of the most important citrus growing areas in Turkey. Groundwater is the main irrigation water source and the groundwater salinization has become an important threat for citrus. This research was carried out to assess seawater intrusion between 1995 and 1997 in Gumuldur-Arapyeri district. Totally 10 groundwater wells, which have been used for irrigation of Satsuma mandarin orchards were selected for sampling from seashore to inland. Three years average of EC and Cl values, Na/Cl, Na/K and SO4/Cl ratios of irrigation water were used to determine the extension and detection of seawater intrusion. Results have revealed that seawater intrusion was effective particularly within 0 - 1050 m.