Organic-inorganic multilayer structures were prepared for a moisture barrier. As the organic polymer and inorganic layers, plasma-polymerized n-hexane and aluminum-oxide layers were utilized, respectively. The plasma polymerization of n-hexane was confirmed by the appearance of carbon double bonds in the produced polymer layer. The organic and inorganic layers were prepared sequentially in vacuum, and the repeated growth sequence produced the multilayer structures. The organic-inorganic multilayer structures show about 35% better moisture-barrier property than those obtained from individual organic and inorganic layers.