the influence of water absorption on the deterioration of carbon fiber reinforced plastics (cfrp) was investigated from the viewpoint of the interfacial change in bonding. carbon fiber braids impregnated with epoxy resin were made and cured. and they were tested by torsional braid analysis (tba) after immersion in boiling water. the followings are the results. (1) the glass transition temperature (t//g) obtained from tba data for cfrp with surface-treated carbon fibers was higher by 22 approximately 36 $degree$ c than that with surface-untreated carbon fibers. this difference of t//g was attributed to the interfacial bonding. (2) t//g dropped with the immersion time of 15 approximately 50 hours, but rose again after the immersion of more than 100 hours. for example, t//g of the after-cured sample with surface-treated carbon fibers dropped from 200 $degree$ c to 146 $degree$ c in 50 hours of immersion, and rose to 174 $degree$ c in 200 hours. from these results, it is considered that, though the fiber-resin interface of cfrp is destroyed by hot water in the early stage of immersion into boilding water, weak chemical bridging is generated in epoxy resin after long immersion. the extent of the bridging is enough to make the strength of the resin higher, but not enough to make the modulus higher. and some new weak bonding is also generated in the fiber-resin interface, making gradual increased in t//g of cfrp (author abstract) 19 refs. in japanese