Abstarct: Geological formations, water-rock interactions and anthropogenic activities such as agriculture and industry are the main factors changing the composition and quality of the groundwater resources in aquifers. Agricultural activities (rice cultivation and citrus) are dominant in the area of Qaemshahr-Juybar alluvial aquifer in Mazandaran province. So, this study was aimed to investigate the geochemical evolution of groundwater in this aquifer of Qaemshahr-Juybar. In this regard, 40 water samples were collected from operating wells at June 2019. Electrical conductivity (EC) and pH values were measured in the field and major and minor ions (nitrate and phosphate) were determined in Water and Environment Lab of the Shahrood University of Technology. baxsed on EC values, the samples were classified into two groups including Group I with EC<2000 μS/cm in which chemical compositions are mainly due to dominant hydrogeochemical processes in the aquifer and Group II with EC values more than 2000 μS/cm at the north of the aquifer where the groundwater overexploitations for agricultural uses caused saline water intrusion from Norther Saline Aquifer. Dominant type of water in Qaemshahr-Juybar aquifer is Ca-HCO3. The quality of groundwater is good in southern parts nearby the carbonate formations, decreasing along the groundwater flow path toward the north due to saline water intrusion and presence of the clay and marl sediments. Geochemical diagrams confirms the occurrence of the water-rock interactions, showing the impact of the dissolution of calcite, gypsum and halite, saline water intrusion and reverse ion exchange in quality and chemical evolution of groundwater in Qaemshahr-Juybar aquifer.