Accurate estimation of the reaeration-rate coefficient is very important for the purposes of dissolved oxygen and self-purification modelling in rivers. The main target of this paper is to evaluate 29 commonly used reaeration-rate coefficient prediction equations, in Sefidroud River, North of Iran, as a case study. In this paper the river’s dissolved oxygen has been modelled involving Streeter- Phelps method. Then the predicted reaeration-rate coefficient results have been compared with four series of collected and measured data of the river. The studied reach of the river has a length of 110km, including 12 water quality sampling stations along that and it is extended from downstream of Sefidroud Dam to the south coast of Caspian Sea. According to the results, among all equations Parkhurst-Pomeroy equation has shown the most accurate prediction of the reaeration-rate coefficient values, with the statistical parameters of Standard Error (SE), Mean Multiplicative Error (MME), Sum of Square of Residuals (SSR) equal to 0.51, 1.05 and 2.35, respectively. Moreover, results indicate that the river has a high Biochemical Oxygen Demand (BOD) and also, a low Self-Purification capacity, during September, which is simultaneous with the seepage of non-point drained agricultural pollutions.