Groundwater is the most important water resource supply for drinking, agriculture and industry in the Meshgin-Shahr, Ardebil province. Therefore, it is required to be considered the quality of the resource beside the quantity. The objective of this study is to identify the hydrogeochemical factors and processes governing the groundwater quality of the Meshgin-Shahr plain using the statistical analysis methods and bivariate diagrams. For this purpose, 25 samples were collected from the groundwater resources of the plain and analyzed in regards with major and some minor (nitrate, fluoride and silica) ions in the Laboratory of the University of Tabriz. The pH and EC values were measured in the field. The results of measurements and analysis show that some parameters in some samples have amounts higher than maximum permissible limits for drinking. Based on the Piper diagram the samples are mainly belonged to bicarbonate and mixed water type. Cluster analysis puts the groundwater samples into two distinct clusters which are different mainly based on the EC and its related ions. The results of factor analysis and different bivariate diagrams revealed that weathering and dissolution of rocks, ion exchange and anthropogenic activities, with different ratios, influence the groundwater composition of the Meshgin-Shahr aquifer.