The drainage system is an infrastructure that requires systematic planning of construction which can function properly to reduce the risk of flooding. Flooding occurs due to the rapid development resulting in lack of permeable surfaces. This will lead to increase the surface runoff, where the flow velocity and flow discharge also will be increased. Therefore, grassed swale is one of the sustainable drainage systems that can be applied to solve this problem. This study aims to identify the effectiveness of the grassed swale drainage system at Universiti Tun Hussein Onn Malaysia (UTHM), to determine the hydraulic characteristics and the effectiveness of vegetation used in the swale drainage system. Through this approach, the solution of past studies, related journals, and Manual Saliran Mesra Alam (MSMA) [1] are used as a reference for this study. Data collection was conducted on grassed swale with total length 60 meters. To obtain an accurate data, measurements of flow velocity have been taken three times, and for three days after raining. Data was observed by 81 times and analyzed using the Manning’s equation. Manning’s equation was adopted to determine the value of hydraulic coefficients for the grass swale channel. The results obtained, demonstrates that the value of Manning’s n for all sections is stated in a range of 0.015 to 0.030. The results also showed a difference in the size of the design, the flow velocity, the water depth, and the flow discharge of the grassed swale drainage system.