Abstract Introduction: It is important to find a simple connection between physic-chemical parameters and indices due to complexity and difficulties of using some indices. This research was performed to determine the relationship between physicochemical parameters and water quality indices Methods: In this research, dominant water type of Gamasyab and GharehSou rivers was first determined using radial diagram. Then, to classify the water quality of two rivers, 14 quality water indices together with national standards for drinking water 1053 and WHO were used. Linear regression was used to determine the relationships between quality indices and physicochemical parameters. Finally, for the accuracy of the results of linear regression, the obtained relationships were tested for two other water sources (river and Gorgan Bay). Findings: Based on hydrochemical results, the predominant type of water in both rivers is Ca-HCO3. Based on diagrams and criteria related to drinking and agriculture, the water quality of both rivers is in the desired range. The results of Langelier, Ryznar, Larsson-Skold and Puckorius indices showed that water quality for the industrial sector was relatively corrosive. Also, the water quality at the study stations is suitable for livestock drinking. The results of linear regression between quality indices with physicochemical parameters of water and some ion ratios showed that the resulting relationships for calculating quality indices can be used for different water types from fresh to saline. Also, comparing the results of linear regression simulations with water quality indicators, indicates the high accuracy of the relationships in water classification for different uses.