Clathrate hydrates, which were formed from methane and cyclopentane, were decomposed by plasma at atmospheric pressure. Methane hydrate was synthesized by injecting methane into shaved ice in the reactor at a pressure of 7 MPa and a temperature of 0 °C. In addition, cyclopentane hydrate was formed by adding surfactant into cyclopentane-water emulsion at 0.1 MPa and a temperature of 0 °C. The process of plasma decomposition of clathrate hydrates has been carried out by irradiating high frequency plasma at the tip of the electrode in clathrate hydrates. 2.45 GHz MW oven and 27.12 MHz RF irradiation were used. This study results gas production that its content identified by gas chromatograph. High purity of hydrogen would be extracted from clathrate hydrate using the in-liquid plasma method.