Abstract Electrical conductivities of type I and IV silica glasses were measured as a function of fictive temperature and water content. Silica glasses with different fictive temperatures were produced by a heat treatment in ambient air and subsequent quenching. The water content in silica glasses was varied by a high temperature hydrothermal treatment. For type IV silica glass, the electrical conductivity decreased and the activation energy increased with increasing fictive temperature. These changes appear to be related to the decrease in specific volume of the silica glass with increasing fictive temperature. For type I glass, the changes were much smaller. Changes in water content produced different effects on electrical conductivities of different types of silica glasses; the conductivity of type I silica glass increased slightly while that of type IV silica glass decreased with increasing water content. These opposite trend in these two types of glasses can be attributed to the different content of aluminum, which interacts with protons introduced by the hydrothermal treatment.