Abstarct: As, the karstic aquifers usually have a better water quality than alluvial aquifers, Ministry of Energy has approved rules to prevent using karstic aquifers in agricultural consumptions, but rather they should be only used as drinking water sources. The present research considers if there is a hydraulic relationship between alluvial aquifers and underlying karstic aquifer in Islamabad Gharb and Zahab plains in Kermanshah Province. Six sets of pumping test data with a constant discharge rate and also 16 step-drawdown data sets are analyzed using professional software aquifer win32 to evaluate the hydrodynamic characteristics of Zahab plain aquifers. In addition, 13 step-drawdown date sets are evaluated using the above mentioned software in order to access the hydrodynamic characteristics of Islamabad gharb plain aquifers. It is noteworthy that, there are both types of alluvial and alluvial-karstic aquifers in these plains. The results show that in both plains, alluvial-karstic aquifers have a higher value of transmissivity, specific capacity and heterogeneity indices than alluvial aquifers, whereas the specific drawdown values of alluvial aquifers are greater than alluvial-karstic aquifers. Some 13 and 11 samples from existing wells in Zahab and Islamabad Gharb plains were respectively taken to study the hydrogeochemistry characteristics, at July 2010. The results show that the electrical conductivity in direction of groundwater flow (i.e. from east to west) in Zahab plain increases from 500 to 900 microhms/cm, whereas, the electrical conductivity in direction of groundwater (i.e. from northwest to southeast) in Islamabad Gharb plain increases from 450 to 800 microhms/cm. Also, these results demonstrate that the degradation of groundwater quality of Islamabad Gharb plain is due to the flow of water through Gachsaran formation outcropping in the middle part of this plain. Also the study of groundwater potential maps, compound and quality diagrams of studied plains shows that there is a hydrogeological relationship between alluvial and karstic aquifers, so that alluvial aquifers are recharged from adjacent karstic aquifers.