Abstarct: The Study area is located in the south east of Tonekabon city in the Mazandaran province. To evaluate the hydrogeochemistry of aquifer and determine the affective parameters affecting the groundwater quality , 23 samples in November 2007 and 24 samples in July 2008 were collected. Electrical conductivity, pH and temperature for all samples were measured on site and the concentration of major ions was measured in the Lab. The defined result show that the concentration of ions near the Cheshmekile River was increased from mountain to sea but in the central area of the plain it is more than other part. this is probably because of presence of water quality diminishing sediment in the central part of the plain . Also Hydrogeological study in this area show that the aquifer in Tonekabon is heterogeneous which may be classified in to three zones., namely east, west and central zones. In the east and west zones because of two rivers, course- grained sediments was deposited but in the central area fine- grained sediments were dominance. Geoelectrical evidences show that the rivers change along times lead to make different sediments in type and size was deposited in this area. However, groundwater quality in Tonekabon is generally suitable for drinking water and agricultural activities. The concentration of Mg and Ca is high and groundwater in this area is in the hard water class baxsed on Todd (2005) classification. Calcite and dolomite saturation index is positive in this area wich may be attributed to microorganism and bacterial activities. By the contrast, Halite saturation index is negative for all samples. The groundwater type baxsed on stiff diagram is bicarbonate Ca and Na.