Shape optimization of free form shell structures with different objective and constraint functions including the stress constraint is the subject of this article. To construct the geometry B-Splines are employed that allow generating smooth free form geometries with a small number of parameters which are considered as the design variables of the optimization problem. For analysis, the finite element method by using the Wilson’s quad shell element is employed. For shape optimization, in each step of the optimization process the mesh generation, finite element analysis, sensitivity analysis and geometry update steps are repeated until convergence. Maximization of the stiffness of structure with volume constraint and the minimization of the weight of structure with the von Misses stress constraint are the addressed problems of this article. In both kinds of problems, the applicates of the control points are considered as the design variables of the shape optimization problem and the sequential quadratic programming (SQP) is employed to solve the optimization problem. Since in this approach, the derivatives of the objective and constraint functions are needed, the sensitivity analysis is carried out in each step by the finite difference method. The quality and smoothness of the obtained results together with the convergence graphs of the presented examples are indicative of the usefulness and efficiency of the proposed approach for shape optimization of shell structures.