Abstract: Due to the harmful health effect of excessive nitrate concentration in human and animal food much research has been conducted on accumulation of nitrate in food plant and water resources. Nitrate concentration in well water of Ardestan region in central part of Iran was investigated during 2005. Ten agricultural districts were selected and in each district 3 to 4 well waters were seasonally sampled. The Nitrate, pH, Electrical Conductivity (EC) and Total Dissolved Solids (TDS) were measured. The results showed that pH is not a limiting factor for irrigation of agricultural land in the present study area. The EC and TDS in all districts were higher than permissible level according to USA EPA and Ayers and Westcot recommendation. Amiran district had the lowest and Charmil district had the highest EC and TDS values. The fall and winter had the highest seasonal TDS and EC values, which may be the results of pumping water in the previous season and deep percolation drainage water. Comparison of wells water nitrate concentrations with the permissible level by Ayers and Westcot for irrigation of agricultural land showed that in Amiran and Rigestan district in some seasons had low to medium and Zavareh-one and -two, Kachurastagh-one and -two, Telk-Abad, Charmil in all season had low to moderate and Hossein-Abad, Najaf-Abad do not have any restriction for land irrigation. Najaf-Abad and Kachurastagh-two had the lowest and highest mean nitrate content, respectively. The highest measured well-water nitrate content was observed during the summer and fall seasons. Also, nitrate concentration of Kachurastagh-one and Kachurastagh-two, Zavareh-one and Zavareh-two, Telk-Abad and Charmill were higher than drinking water standards.