Chemotaxis is the biased movement developed by certain living organisms as a response to chemical gradients present in their environment. Thanks to advances in the computing field, bacterial chemotactical strategies and its excellent ability in searching can be modeled, simulated and emulated, thus developing bio-inspired optimization methods alternatively to classical methods. In this work, a multi objective optimization algorithm based on bacterial chemotaxis is proposed and applied to the shape optimization of shafts. Design variables are the diameters along shaft’s length and different constraints are tested, such as variable torques, critical velocities, and position of elements. The design results are obtained in terms of final weight and design safety factors at specific points of the shaft, thus leading to a front of optimum solutions, i.e. to the different possible design solutions that satisfy design constraints, where the engineer can find the best compromise solution for his application.