: Dissolved oxygen is essential to healthy streams and lakes. The dissolved oxygen level in an indication of how polluted the water is and how will the water can support aquatic plant and animal life. A higher dissolved oxygen level indicates better water quality. There is a significant oxygen transfer associated with most hydraulic structures because the air entrained into the flow is split into small bubbles, which greatly increases the surface area for transfer. Stepped cascades are particular instance of this, and the aeration efficiency of such structures should be studied in the laboratory. In this paper, the aeration efficiency of stepped cascade with and without end sill was investigated in comparison with smooth cascade which taken as a reference in a large laboratory flume. Dissolved oxygen concentrations were measured versus different discharges in range (4.6-24.6) L/s. The end sill height was varied as a percentage of the step height of the stepped cascade (25%, 50%, 75%, and 100%). The results indicated that stepped cascades are very efficient at oxygen transfer because of the strong turbulent mixing associated with substantial air bubbles entrainment and that this advantage becomes more pronounced in nappe flow regime. The highest aeration efficiency was achieved in the case of 3 steps cascade with 100% end sill height with average percentage 45%.