Abstarct: The Ziarat River is one of the tributaries of the Qarahsu catchment, and a part of this river flows through Gorgan City. In order to study the environmental hydrogeochemistry of this river, 11 water samples were collected in June 2013. Physic-chemical parameters (pH, electrical conductivity, TDS), the concentrations of major ions and some mextals (Fe, Cu, Al, Cr, Pb, Mn) and biological parameters (dissolved oxygen, biological oxygen demand, chemical oxygen demand and coliform bacteria) were analyzed by standard methods. The obtained results show that pH of the water samples varies from 7.20 to 7.88, and the highest pH is observed near the discharging point of cowshed effluents. The electrical conductivity of the water samples varies from 701 to 1422 μs/cm and the highest value is observed near the Ziarat hot spring. Major ions concentrations of the most samples are in permissible limit for drinking. baxsed on the calculated saturation indices, ion ratios and Gibbs and Durov diagrams, the chemistry of waters is dominantly controlled by the dissolution process. According to Stiff and piper diagrams, it was found that water type in upstream and downstream is Ca - SO_4 and Na-Cl, respectively, probably due to effect of natural and anthropic factors. baxsed on Schoeller and Wilcox diagrams, all water samples are suitable for drinking and agricultural purposes, respectively, baxsed on magnesium hazard index, most of the samples are not suitable for agricultural usages. According to calculated values for residual sodium carbonate and sodium percent parameters, all samples are acceptable for irrigation. In some stations, the concentrations of iron and aluminum are higher than WHO standards for drinking uses, which is due to the anthropogenic activities. Calculation of mextal index shows that most of the samples are polluted with mextals. baxsed on calculated values for HEI, HPI and C_d indices, samples collected within the Gorgan City reach have the highest mextal pollution, which is due to the discharge of urban wastewaters. The obtained results indicate that the amounts of dissolved oxygen in all samples are in permissible limit. In some stations, BOD and COD levels are higher than permissible values and the highest amount of these parameters is observed near the discharging point of cowshed and agricultural effluents. The results show that all water samples are microbically polluted and the lowest microbical pollution is observed in upstream. Water Quality Indices (NSFWQI and OWQI) show that all studies samples are placed in bad and very bad calsses.