Background and purpose: Nitrate is one of the most important water pollutants contributing to methemoglobinemia in children and stomach cancer in adults. The aim of this study was to investigate the nitrate contamination of groundwater in Shahrood and Damghan and determination of the spatial pattern of its distribution.

Materials and methods: A total of 154 wells were sampled in shahrood and Damghan and the nitrate concentration was analyzed. Kruskal-Walliss test was applied to compare the concentrations of nitrate in urban, rural and plain areas. The nitrate concentrations in agricultural and drinking wells were compared using Mann-whitney test. Empirical bayesian kriging method was used to study the spatial distribution of nitrate in the groundwater.

Results: The mean concentration of nitrate in urban, rural, and plain area wells were 29.18, 11.58, and 10. 40 mgl^-1, respectively. There was a significant difference in nitrate concentration between urban areas and that of the rural and plain areas but no significant difference was found in nitrate concentration between the drinking and agricultural wells. The geostatistical analysis showed higher concentration of nitrate in southern part of the area than that of the northern part.

Conclusion: The concentration of nitrate was higher than the permissible levels in 4.5% of the studied wells however, at present this is not considered a health risk in the region.