Atomization is affected by the internal flow of liquid in the nozzle as well as the interaction between liquid and the surrounding air at the spray downstream. Cavitation which is generated in the nozzle is known for having a strong influence on atomization. Recent research shows that cavitation in the circular nozzle had a cylindrical shape that is symmetrical to the nozzle axial However the cavitation shape of elliptical nozzles looked like a horseshoe in that the cavitation length for the major axis plane is longer than that of the minor axis plane. The purpose of this study is to numerically investigate the internal nozzle flow and cavitation characteristics in a circular nozzle and an elliptical nozzle. The computational fluid dynamics (CFD) code FLUENT 6.2 was used to perform the numerical simulation of the cavitating flow in the nozzles. A comparison between the cavitation shape of the numerical results and those of the experimental results was made to validate a numerical solution. As a consequence of this study, in the case of the elliptical nozzle, the static pressure of the working fluid at the major axis plane was decreased near the vapor pressure along the orifice wall at a longer distance when compared with the minor axis plane. Also, the radial velocity distribution was different between the major axis plane and the minor axis plane when the working fluid was flowing into the orifice inlet.