Abstarct: The Study area is located in Romeshgan plain, southwest Kuhdasht County of Lorestan province. In this area the main water’s supply is from groundwater’s reservoir. There is no general research for estimation of groundwater quality of this plain. The purpose of this research is to assessment the role of geological factors and agricultural activities on the groundwater quality in Romeshgan plain. For this purpose, groundwater sampling was performed. Electrical conductivity (EC), acidity (pH) and temperature was determined in the field. Water samples were analyzed by standard methods for major cation and anion contents. baxsed on EC values, Romeshgan plain was divided to three zones. The average EC value in east, central and west of the plain are 626, 846 and 1226 micromohs/cm, respectively. The lower electrical conductivity (EC) in the east part of the plain, is probably due to the recharge of the plain by limestone units. In the central zone, the higher EC values of groundwater is probably due to the high exploit of groundwater. In the west zone of the plain, the exposure of Gachsaran formation has probably led to the highest electrical conductivity (EC) of the water samples. Thus, geological factors are the main reasons for destruction of water quality in the west zone. In order to assess the influence of agricultural activities on groundwater quality, nitrate concentration of water samples was determined. The higher concentration of nitrate in central zone is mainly due to the higher agricultural activity in this part of the Romeshgan plain.