The ionic conductivity of AgBr-montmorillonite composites from 0.9 to 30 volume percent in montmorillonite was studied in the range from 20 to 410 degreesC. A remarkable increase in the conductivity at low temperatures is found. At 20 degreesC a maximum value about 45 times higher than that of pure AgBr is reached at 2.6 v/o. A noticeable effect of humidity is also found. The results are qualitatively explained on the basis of the model proposed by Maier for heterogeneous doping of solid electrolytes.