In this investigation, a technique to determine effectively an optimum shape of an axisymmetric body is suggested. The technique is a sequential search method consisting of the following two steps. In the first step, the superiority or inferiority of a given shape, which satisfies the design constraints, is judged by the deviation from the stress provided with a design object. In the second step, this given shape is modified by the proportional transformation method of the elements used in the finite element method. By the iteration of these steps the optimum shape will be obtained. As the application of this iterative method the optimum shapes of the thick-walled vessels under internal pressure will be obtained.