Abstract: For degreasing a honeycomb core, the honeycomb core is placed in a degreasing chamber, which is then closed. The degreasing chamber is thereafter evacuated to a vacuum in the range of 50 to 100 torr, and the upper and lower surfaces of the honeycomb core are sprayed with a normal paraffin as a hydrocarbon cleaning agent heated at a temperature of from 60.degree. to 120.degree. C. for shower rinsing and finish shower rinsing. The internal pressure of the degreasing chamber is adjusted to a vacuum in the range of 30 to 40 torr, and a vapor of the normal paraffin cleaning agent heated at a temperature in the range of 110.degree. to 120.degree. C. is supplied into the degreasing chamber for vapor degreasing of the honeycomb core. Finally, the honeycomb core is dried in the degreasing chamber at a temperature of from 70.degree. to 120.degree. C. under a reduced pressure in the range of 0.1 to 10 torr.