Abstarct: The study area (Arkan,s plain) is located in south west of Bojnourd. The most important formation in the study area are Lar, Shorije, Tirgan, and Neogen deposite. In order to study the hydrogeochemical characteristics of the region, all boreholes and springs in the study area were sampled. The values of electrical conductivity, water temperature and pH were measured in the field, and the value of major ions (including Ca2+, Mg2+, Na+, K+, HCO3-, SO42-, Cl-, NO3-) were measured in the laboratory of Park of Science an Technology of Semnan province (Shahrood). The obtained results indicate that the groundwater quality in the direction of flow toward the south and south-east is considerably reduced. Such that the value of electrical conductivity in the upstream of the study area (adjacent to the limestone aquifer) is around 320 micromhos/cm and it is increased to 1500 micromhos/cm in direction stream of underground water. According to boreholes logs and the lithology of the study area, it may be argued that the main reason for decreasing the ground water quality in a short distance is presence of gypsum, shale and marl of Neogen deposits. To evaluate the hydrodynamic parameters of the aquifer pumping test data of boreholes were applied. In order to analyse the pumping test data (constant rate and step-drawdown tests) the Aquiferwin32 Software were used. The obtained result indicate that the value of transmissivity vary between 355 and 687 sq. m/day. that this variations which reveals that the heterogeneity of aquifer. Moreover, the data from 79 electrical sondage in study area from 7 geoelectric profile were used and interpreted. On the basis of obtained result from geoelectric studies and the geology of the region, three distinct strata were recognized. These strata from ground surface to the depth are recent alluvium deposits, marl and conglomerates of Neogen, and limestones of Tirgan.