Abstarct: Groundwaters in the arid and semi-arid regions like Iran, where the average rainfall is less than one-third of Earth's average rainfall, are very important for different uses. Nevertheless groundwaters are at risk of contamination. Nitrate ion has long been considered as a chemical indicator of water pollution. The main sources of entered nitrate into the groundwater are municipal and domestic sewage and agricultural activities. The aim of this study was to study the hydrochemical characteristics and spatial distribution of nitrate in Damghan plain. For this purpose, 39 wells were sampled in July 2016. EC and pH in the field and major ions in the laboratory were measured. Damghan plain is recharged mainly from the West and finally discharged to the desert plains of Haj Ali Quli in the East. Electrical conductivity has increased in the groundwater flow direction from the recharged zone in the West to the East. But the existing anomalies in electrical conductivity map result from the intrusion of saline water from the salt pan of Chah Jam in Northeastern and evaporate deposits of northern plain. The water types in recharged zone are mainly HCO3-Ca to Cl-Na which is changed into Na-Cl and Ca-Mg-Cl, in central area of the plain. But in the northern part of the plain, the water type is SO4-Ca due to the dissolution of evaporate formations. baxsed on measured nitrate concentration in 32 wells the minimum value was 2.6 mg/lit and the maximum value was 71.8 mg/lit in the center of the city. The highest values belonged to urban areas due to shallow depth of ground water and waste water leakage into ground water while agricultural activities have a minor role.