Abstract: Background and Objective: Surabaya river has been polluted by many industries, which is located along the river and by sewage from human activities. Wastewater effluent, which has not met the established quality standards has been discharged into water bodies. Surabaya river is the main source water for clean water and drinking water consumption. The aim of this study are to identify water quality of Surabaya river along Karang Pilang-Gunung Sari segment and to assess organic parameters of river water quality with Streeter-Phelps model to predict its quality for further monitoring. Materials and Methods: Organic parameters such as; Dissolved Oxygen (DO) and Biological Oxygen Demand (BOD) were analyzed in addition of pH and temperature parameters. Sample was taken in Surabaya river between Karang Pilang-Gunung Sari Segment during wet season. Streeter-Phelps model was used to apply the data modelling and chi-square was applied to validate the data statistically. Results: The results show that along the segment has low DO concentration averagely (2.7±0.1 mg L–1), even DO<0.5 mg L–1 has been detected. Low DO indicated a high BOD concentration (50.5±1.5 mg L–1). For the purification process itself, the deoxygenation value (K1) is 0.34-0.36/min, while the reaeration value (K2) is 0.80-1.1/min. Conclusion: Comparison between organic parameters measurement and modelling indicated that Streeter-Phelps model could be applied to monitor water quality of Surabaya river. The validation (sig = 90%, Xi2 < X2) shows chi-square value 1.39<7.79 for BOD and 2.96<7.79 for DO concentration.