Abstract: This paper presents gemmological study on hydrothermal treatment of ambers in pressure furnace.Conclusions are following as:(1) Hydrothermally treated amber raw materials have a new yellow-white or yellow-green layer under the natural weathering skin; locally, various holes and newly-grown black or yellow-white scabby crust appeared; (2) Hydrothermally treated ambers have the white round "cooked scar" on the surface; (3) Hydrothermally treated ambers have abundant gas-liquid inclusions with small and flate bubbles forming cloud-like effect; (4) The scanning electron microscope result showed that there are dense bubbles of various sizes accompanied by stress fractures hydrothermally treated ambers.This study emphased the identification of hydrothermally treated ambers requaire multiple evidences, including the key scabby crust and evaporation spot.