We present the first study of the microscopic dynamics of confined supercritical water. Our results have been obtained by molecular dynamics simulations of supercritical water adsorbed inside carbon nanotubes. Water-water interactions were accounted by means of a flexible simple point charged potential whereas water-carbon interactions were modeled by Lennard-Jones forces. Diffusion coefficients and relaxation times of water molecules have been analyzed. Absorption lineshapes indicate that microscopic dynamics is dominated by a competition between confinement and thermal effects. (C) 2002 Published by Elsevier Science B.V.