Abstract. The paper deals with minimum weight design applying Evolutionary Strategy (ES), improved by controlled mutation. Applied selection and crossover are typical for ES. Mutations, however, are controlled by state variables, in this case by stresses. After crossover, from each population, a voted number of chromosomes are inspected from the point of view of stresses occurring in structural members (genes). Changes of cross-sectional areas are introduced depending on the minimum, or maximum stresses. 124 runs of the algorithm were performed on a bench-mark problem, with known optimum solution. The number of exact solutions, applying controlled mutation, was four times larger than in the case of a simple ES algorithm.