The use of zeolites as an adsorbent for water or ammonia in heat pumps and cooling systems is an interesting alternative to the traditional refrigerants. Recently, zeolites are also in discussion as hydrogen storage material. For all these applications the effective thermal conductivity of the zeolites is an important thermophysical property. The effective thermal conductivity lambda(eff) was measured by using the transient hot-wire method with an accuracy of +/-5-15%. The accuracy increases with increasing effective thermal conductivity. Hydrogen, argon, helium, nitrogen and air were used as filling gas. The gas pressure was varied in the range of 1 mbar less than or equal to p less than or equal to 30 bar and the temperature in the range of 210 K less than or equal to T less than or equal to 570 K. A simple model is proposed to calculate the effective thermal conductivity of the zeolite powder with an accuracy of about +/-30%.