The spatial evolution of local complex conductivity across a grain boundary of hafnia has been measured using energy filtered high-resolution transmission electron microscopy and valence electron energy loss spectroscopy (HRTEM-VEELS). A local increase in the real part of the conductivity and the effective electron density inside the grain boundary is clearly evidenced. This methodology could be advantageously used to study the leakage pathways and the regions susceptible to early dielectric breakdown in the most advanced dielectric stacks, to further optimize the technological developments of this highly demanding industry.