We have studied the conductivity relaxation of fluoride glasses in the system with NaF content ranging from 5 to 30 mol% in the frequency range 10 Hz-2 MHz and in the temperature range from 300 K to just below the glass transition temperature. The conductivity decreases with the increase of NaF content in the compositions, which is shown to result from the lower and lower decoupling of the ions from the viscous motion of the glassy network. Small values of the stretching exponent are observed for the present glasses and have been associated with the high cooperation between the ions in the conductivity relaxation process.