CaCu3Ti4O12 bulk and thin films are prepared su ccessfully by solid-state reaction and pulsed laser deposition (PLD). Dielectric constants ε′ (1kHz,300K) higher than 14000 are found in both types of CaCu3Ti4O12 materials, which is the best result in this system. We first report the c-axis-oriented epitaxial CaCu3Ti4O12 thin film and i ts dieletric properties.Such a high dielectric constant does not depend much upon temperature in the range of 100-300K,showing that this material has high thermal stability.The behaviour of dielectric conductivity σd against frequency can be well ex plained in terms of the hopping mechanism.