For helium cooled pebble bed blankets, the description of the thermal-mechanical interaction between pebble beds and structural material requires the knowledge of the pebble bed thermal conductivity k as a function of temperature T and deformation state (pebble bed strain ɛ).Experimental results for the thermal conductivity of compressed beryllium pebble beds are presented. The pebble beds consisted of 1mm NGK pebbles and are representative for dense pebble beds (packing factors γ≈63.5%). Measurements were performed in the temperature range between 200 and 650°C, with maximum pressures of 3.6MPa and pebble bed deformations up to ɛ≈3.5%. A correlation is proposed which is based primarily on measurements but uses conductivity values for non-deformed pebble beds predicted by the Schlünder Bauer Zehner model. It is argued that the proposed correlation is expected to be applicable also for pebble diameters different from 1mm and other packing factors than 63.5% as long as densified pebble beds are considered.Finally, a conductivity correlation is presented which is applicable up to the ultimate compaction to a solid body.