Groundwater is a vital natural resource for the economical and secure provision of potable water supply in both urban and rural environments. It plays a fundamental role in human well-being, as well as that of many aquatic ecosystems. The rapid growth of urban areas has supplementary effects on the groundwater quality due to over-exploitation of resources and inappropriate waste disposal actions. The sources of pollutants that cause groundwater contamination are different; in addition to natural processes, practically every type of human activities may eventually cause a loss on groundwater quality. The Mashhad plain is located in the north-eastern of Iran, in heavily polluting sources and a serious threat for the health of groundwater supplies resources. This paper identified the major sources of groundwater pollutant and estimates their contamination potential in the Mashhad plain unconfined aquifer. In this research, at first, a list of the most important contaminant sources in the Mashhad plain has been prepared. For this purpose with the collection of information regarding potential pollutants in the area and with field surveys, monitoring, sampling and analysis of water and pollutants, the volume of pollution and the risk level of contaminants is determined. The results showed the highest pollution potential in the case-study area is belong to population centers and then industries in the Mashhad plain. It should be noted that the analysis of samples was conducted in 2012 and all the information, maps and statistical tables presented in this article, have been taken from studies in the regional water company of Khorasan Razavi.