R. Feynman said that there’s plenty of room at the bottom, which is widely regarded today as the original inspiration for the origin of nanoscience and nanotechnology. Thus, those who control the materials will control the technology in the 21st centuries. There have been so many new functional materials developed so far. When we control the materials in the range of 1 ~ 10 nm, there are so many different characteristics by discontinuity in properties, so that this will induce the innovation for all the industries. In this sense polymer nanocomposites will be one of the favorite materials for NT. The properties of polymer nanocomposites are very different from those of polymer composites, which incorporate the fillers of larger than 100 micron in size. I will discuss a few peculiar properties observed in them and finally their future applications to energy sources. Polyhedral oligomeric silsesquioxane (POSS) is the perfect nanoparticle for the organic polymers due to its real organic-inorganic nanohybrid nature. It has two important properties such as high strength of inorganic materials and easy tailoring of properties for the given polymers. In this presentation I will discuss how to design the polymer nanocomposites as solid electrolytes for all solid-state Li batteries and fuel cell vehicles, each.