An ammonium polyphosphate composite with high ionic conductivity was prepared. A thermal gravimetric analysis was performed. Investigations by impedance spectroscopy were carried out in dry and humid atmospheres. The conductivity was found to be remarkably high in a water-rich environment (less than or equal to 0.1 S cm(-1) at 573 K). (C) 1999 Published by Elsevier Science B.V. All rights reserved.