Abstract: In this paper a method for equi-strength design of statically indeterminate beams is presented, based on the principle of minimum complementary energy. And an analytical expression is derived for the stiffness variation of single or multi-span beams under the application of arbitrarily distributed loads, concentrated forces and couples. Illustrated examples concerning beams with fixed width are riabbe height or sandwich beams with variable thickness of outer sheets are also given. The comparison with reported results shows the effectiveness of the proposed method.