A method is presented for solving three dimensional inviscid internal flows, with application to three dimensional noncircular nozzles. Spatial discretization is made on the finite difference formulation of Euler's equations. The convective terms is differenced using the Van Leer flux vector splitting technique. Time is advanced using the implicit Euler backward time stepping. The resulting system of algebraic equations is solved using ADI method. New numerical treatment of the flow boundary conditions is presented and applied to handle the complicated mixed boundary conditions. Application to solve flow through nozzles shows good agreement with analytical results.