The downcomer for solids recycle is a key component in circulating fluidized beds. In the case of fast fluidization, the solids circulation rate through the downcomer is quite large compared with that in the conventional cyclone dipleg, resulting in a certain amount of gas flow entrained by downflow of solids, which changes the behavior of the gas-solid flow. The entrained gas flow rate in the downcomer incorporating a riser was determined by using a gas tracer technique. The entrained gas rates for different particle properties, solids circulation rates as well as aeration gas rates were measured and a hydrodynamic correlation was established. The transition in the flow pattern was also observed. These results are expected to provide a basis for the design of the downcomer.