The major aim of the present study is to evaluate the surface water quality at a part of the Damietta branch, Nile River of Egypt via the measurement of some physicochemical parameters followed by calculation of water quality index (WQI). WQI is considered a simple and effective tool successfully applied for the assessment and investigation of the status and quality of the surface water in any ecosystem. A total of 21 parameters was monitored and measured at ten stations for a year from January to December 2014. Correlation coefficients for physicochemical parameters showed that only turbidity, dissolved oxygen, biochemical oxygen demand, ammonia, and silicate had spatial significant variability. Almost the highest average values appeared at station III. The calculated WQI manifested that the highest value was 66.70% at station IX, while the lowest was 56.44 % at station III. One-way analysis of variance (ANOVA) showed that water quality in the autumn season was higher than the summer months while the spatial significant variability of the WQI confirmed that the St.III. recorded the worst sites, while the sites of the East Bank had; almost the highest average values appeared Generally, most stations found in a medium quality. Damietta branch eastern bank was better than the western one. The mean values of most measured parameters were within the threshold limits in comparison to Egyptian environmental standards regularities (EESR). WQI will be useful mechanism for regular monitoring.