Water quality and its enhancement depend upon the level of dissolved oxygen present. In fact, the oxygen concentration in surface waters is a prime indicator of the water quality for human use as well as for the survival of aquatic biota. There are many different hydraulic structures that have been employed to improve aeration purposes. The aeration efficiency of such structures should be studied in the laboratory. Stepped cascades are particular instance of this, in this paper, the aeration efficiency of stepped cascade with and without end sill at inclination angle = 15˚ was investigated in comparison with reference model which taken 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 submerged sill was placed at different locations (20.0, 40.0, 60.0, and 80.0 cm) in the stilling basin after the stepped cascade structure. 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 2 steps cascade with 50% end sill height and submerged sill at 60.0 cm after the model with average percentage 83%.