Rosetta branch is one of the two main branches in Nile delta and El-Rahawy drain is one of this main sources, which outlet on the branch. It is subjected to many sources of pollutions from municipalities, agriculture and industry, but only little information is available on the quality of river water. The aim of this study was to analyze the river water quality in Rosetta branch at the outlet of El-Rahawy drain, Nile delta. Water samples were collected seasonally from El-Rahawy and Rosetta branch and the following physicochemical parameters were analyzed: hydrogen ion concentration (pH), total dissolved solids (TDS), electrical conductivity (EC), dissolved oxygen (DO), ammonia (NH3), total alkalinity (CO3+HCO3); biochemical oxygen demand (BOD) and chemical oxygen demand (COD). The results were compared with the water quality standards of Egypt (Law 48/1982), FAO and Canadian Water Quality standards (CWQGs). Statistical studies were carried out by calculating correlation coefficients between different parameters. The large transports of NH3, and TDS with low COD, BOD and DO values along El-Rahawy drain were seriously deteriorating the water quality in the downstream of Rosetta branch, especially during the low flow condition in winter.