Abstarct: Agricultural activities are known as one of the reasons for the decline of groundwater quality in the world. Aleshtar plains is an areas with extensive agriculture in the Lorestan province and thus susceptible to pollution from agriculture practices. This study with the aim of investigating agricultural impacts on chemistry of Aleshtar aquifer has been done. In order to evaluate quality of Aleshtar aquifer, 29 wells and 4 springs were sampled in June 2016. Electrical conductivity (EC), pH and temperature were measured in the field and major ions and nitrate in laboratory. According to spatial variations of electrical conductivity, groundwater samples in the Aleshtar aquifer were divided into two separate groups. First group includes samples with electrical conductivities less than 450 µs/cm in which chemical behavior is mainly influenced by dominant hydrogeochemical process in the aquifer due to greater distance from the river and deeper groundwater level. Second group includes samples with electrical conductivities more than 450 µs/cm in which due to decreasing depth to water table, the chemical behavior is mainly influenced by the evaporation process. Ca-HCO3 is dominated type of groundwater in the aquifer. Nitrate concentrations in Aleshtar aquifer are also divided into two separate groups. First one (EC< 450 µs/cm) include samples located in areas with intensive agriculture as the increase in nitrate is due to agricultural activities. Second group (EC> 450 µs/cm) with higher variations in nitrate concentrations is also divided into two subgroups G2A and G2B. The samples in G2A have high electrical conductivity and nitrate due to the evaporation. The samples in G2B have high electrical conductivity, but nitrate concentrations have been decreased due to the denitrification process. The results show that nitrate concentrations are above the standard limit for drinking water (45 mg/l) in three sample. Nitrate is highly correlated with calcium, chloride and bicarbonate which confirms its origin from agricultural activities.