Decomposition of epoxy resin was carried out with sub- and supercritical water in the temperature range of 300-450degreesC. At 350-380degreesC and 25 MPa, about 90% of the resin was decomposed to water+methanol-soluble components, including low molecular weight products and monocyclic phenol compounds such as phenol and iso-propylphenol. Water in the reactor was found to inhibit the coking and enhance the decomposition of the resin, compared with the case of pyrolysis, in which the yield of THF-soluble components of high molecular weight exceeded 50%. Using supercritical methanol, the epoxy resin was partly decomposed, but the yield of products of low molecular weight was lower than that using supercritical water. Carbon fiber reinforced plastic (CFRP), which is composed of carbon fiber and epoxy resin matrix, was treated with supercritical water at 380degreesC and 25MPa to examine the industrial applicability of this method. As a result, clean carbon fiber was recovered and the resin was decomposed and removed from the carbon fiber.