As a fuel benign to the environment, hydrogen has attracted much attention in recent years. Currently, hydrogen is commercially produced from the steam reformation of natural gas and coal or from the dehydrogenation processes in petroleum industry. There are investigations on processes such as the steam reformation of glucose and methanol, enzyme-catalyzed decomposition of sugar, alcohol partial oxidation, and photo-catalytic decomposition of biomass and water. Herein, we demonstrated that hydrogen could be produced from the direct decomposition of methane, ethane, asphaltum, and polyolefins over molten magnesium. The Mg catalyst showed high activity and high hydrogen selectivity. After the reaction, the Mg found evaporated and condensed at the top cold section of the reactor can slide back to the reactor simply through heating and melting of the condensed metal.