Abstarct: Bastam Plain with an area of 1330 km2 is located north of Shahrood city on geographical coordinates of 〖55〗^0 E to 〖55〗^0 〖30〗^' E longitude and 〖36〗^0 N to 〖36〗^0 〖30〗^' N latitude. The existing groundwater in this area is of vital importance. The groundwaters in the area are extracted by 330 water wells which are used for agricultural and drinking water. The saline waters and salt plain exist in west and east of the plain. Therefore most of the water wells are concentrated around Bastaam city and southwest of the plain. The main purpose of this study is to assess the hydrogeological and hydrogeochemical properties of Bastam aquifer. The data from water level variations in 16 piezometer wells are used In order to study the hydrogeologic properties. The general groundwater direction is North West and south west towards south east of Bastaam Plain, which indicates that the aquifer is being recharged from the North West and southwest. In order to investigate the ground water level variations, the unit hydrograph of the plain was drawn from 1379 to 1392. During this 14 years period, there has been a fall of 13 m in ground water level, so that maximum fall occurs at the central, south western parts and the surroundings of Bastaam city and the minimum fall is at the western and eastern parts of the area. baxsed on the hydrochemical analysis of 22 operating wells, the ground water quality is affected by aquifer water withdrawal and intrusion of saline water in surrounding formations; So that the northern and southern parts of the plain have minimum electrical conductivity, while most western and eastern parts, have the maximum electrical conductivity. High rate of electrical conductivity in these areas is a natural and obvious issue.