As bioretention systems,rain gardens can mitigate the adverse impact of urbanization on hydrolo-gy and water quality; but its performance is affected by many factors including the existing forms of pol-lutants and the internal hydraulic characteristics of rain gardens. This paper presents an experimental studyon hydrological processes and the water quality improvement of retaining road surface runoff with a rain gar-den in loess region of China. We analyzed the variation of dissolved and particulate nitroge...