Abstract The paper considers the problem of optimization of the box section of the main girder of the single-girder bridge crane. Reduction of the girder mass is set as the objective function. The constraint functions are the criteria of strength, local stability of plates, lateral stability of the girder, stiffness, dynamic stiffness, as well the constraints of cost effective design. Methods of the following biologically inspired algorithms were used for the optimization: Firefly Algorithm (FA), Bat Algorithm (BA) and Cuckoo Search algorithm (CS). The obtained results of optimization were compared with several solutions of single-girder bridge cranes, which verified the optimization method. The paper presents the advantages and weaknesses of the methods applied to the concrete solutions of single-girder bridge cranes.