This paper presents the results of experimental investigation and Computational Fluid Dynamic (CFD) analysis of an air-air subsonic ejector. The CFD modeling is used to investigate the effect of mixing chamber length and area ratio (ratio of nozzle area to mixing chamber area) on the performance of the experimentally tested ejector. For short mixing chamber to diameter ratio MC=1.76 it is found that the separation region in the annular part occurs along the whole length of mixing chamber and extends to 60 percent of the diffuser length and the flow reattaches at an axial distance to diameter ratio X/D= 5. Increasing the mixing chamber length to MC=4.76, 6.76, 9.76 and 14.76, reduces the area of separation and the reattaching flow begins at an average value of axial distance X/D= 3.25. Increasing the MC to a value more than 6.76 has no meaning in the mixing process as it increases the friction losses in the mixing chamber. Increasing the area ratio from AR1=0.057 to AR2=0.171, the massive recirculation zone in the mixing chamber is reduced by about 50 percent and the pressure ratio increased by 21 percent with increasing the efficiency by 22 percent. Finally, the numerical performance curve agrees well with the experimental one.