It is, shown that the contributions. of electronic and ionic charge carriers to the grain boundary conductivity can be separated by selectively blocking one of the carriers. In this way, the electronic and the ionic partial conductivity at the grain boundary of a 0.016 wt % Fe-doped SrTiO3 bicrystal were determined in the temperature range of 600 to 700 K and in argon. Contrary to the bulk where the electronic and the ionic partial conductivity are comparable, the grain boundary was found to be almost exclusively electronically conductive, being in agreement with the expected more severe depletion of oxygen vacancies in the space charge layers.