The aim of the present study is to investigate the performance of jet pump. The effect of geometrical and operational parameters on the jet pumps efficiency were determined numerically and experimentally. Numerical investigation was held firstly to determine the effect of diffuser angle, mixing chamber length, pump area ratio and driving nozzle position on the jet pump efficiency. Commercial computational fluid dynamics (CFD) solver ANSYS R 15.0-FLUENT using SST-turbulence model was used. The numerical results showed that jet pump efficiency increases with decreasing both of diffuser angle and mixing chamber length up to a certain value and then pump efficiency decreases. Also, jet pump efficiency increases with increasing pump area ratio up to a certain value and then pump efficiency decreases. It was found that maximum computed efficiency is 37.82 % at the pump area ratio of 0.271 and a pressure ratio of 0.317. In addition, the numerical results showed that the optimum relative length of mixing chamber is 5.48 and the optimum value for diffuser angle at which the efficiency is a maximum value is 5º. Experimental tests were conducted to study the effects of various geometrical and operational parameters on the performance of the jet pumps. A test rig was constructed using the optimum design from the numerical results. The physics of flow within axial-water jet pumps can be analyzed and optimized easily by using the CFD, 2D technique with a satisfactory accuracy in order to save computational time and cost. The CFD's results were found to agree well with actual values obtained from the experimental results.