The conductivity of rapidly quenched glassy flakes in the system Li₄SiO₄-Li₃BO₃ was measured. A maximum conductivity was observed at a composition near 50-60mol% Li₃BO₃; this behavior can be called the “mixed anion effect”. The enhancement of conductivity was shown to be related to the decrease in the activation energy for conduction. The relation between the “mixed anion effect” and the degree of supercooling of glass was discussed on the basis of the linear plots of the conductivity enhancement vs. the ratio (T₁-T_g)/T₁, where T₁ is the liquidus temperature and T_g the glass transition temperature.