MAZANDARAN CATCHMENT AREA, WHICH IS THE IMPORTANT BASIN IN IRAN, FLOW FROM THE NORTHERN ALBORZ ATTITUDES LIKE: ARAS, SEFIDRUD, CHALUS, HARAZ, SEHEZAR, BABOL, TALAR, TAJAN, GORGAN, ATRAK, QARASU AND NEKA. MONTHLY MEASUREMENTS OF WATER QUALITY VARIABLES SUCH AS EC, NA, CA, MG, K, CL-, SO4, PH, WERE MONITORED AT DIFFERENT STATIONS OF THE MAZANDARAN CATCHMENT AREA FOR THE PERIOD FROM 1966 TO 2006. USING THESE DATA THE WATER HAS BEEN ASSESSED AS DRINKING WATER AND IRRIGATION WATER COMPARED TO THE STANDARDS. FOR THIS PURPOSE, FIRSTLY, THE MEAN VALUE OF PARAMETERS HAS BEEN CALCULATED FOR EACH STATION. SECONDLY, THE QUALITY OF WATER ALONGSIDE THE RIVER HAS BEEN ASSESSED.THE PRESENT WORK HAS BEEN WITHIN THE FRAMEWORK OF THE PANTARHEI RESEARCH INITIATIVE OF THE INTERNATIONAL ASSOCIATION OF HYDROLOGICAL SCIENCES (IAHS).