The design of straight labyrinth seals for a steam turbine has had little progress concerning their geometry. As an auxiliary system, its current shape causes a significant loss of efficiency in this machine. Therefore, this study evaluates the application of an automatic optimization process to define more suitable seal profiles that increase the pressure ratio at each turbine stage. Multidisciplinary software, controlled by a Multi-Island Genetic Algorithm (MIGA), has been coupled to optimize the seal shape of a steam turbine used for geothermal operation. By parameterizing the seal geometry, the leading edge was automatically manipulated with the numerical algorithm, obtaining a tendency of its shape towards 45° at the tip to the leading edge of the steam, which decreased the outlet pressure of the seal system by 5%. It is inferred that this practical methodology could easily update the seal design during the turbine re-powering operations.