The dielectric properties of the one-dimensional (1D) water clusters confined in the porous crystal, [Co-3(2,4-pydc)(2)(mu(3)-OH)(2)]center dot 9H(2)O, were examined. The dielectric constant (epsilon') decreased abruptly below 200 K, where the first-order phase transition occurred. The results of molecular dynamics simulations suggested freezing of the molecular motion of the guest water molecules, forming 1D water clusters at 200 K. epsilon' (10 kHz) increased sharply above 300 K and became as high as 500 at 383 K. The hysteresis loop observed at 340 K indicated the antiferroelectric state of the guest water system.