Non‐uniform structures of nuclear matter are studied in a wide density‐range. Using the density functional theory with a relativistic mean‐field model, we examine non‐uniform structures at sub‐nuclear densities (nuclear “pastas”) and at high densities, where kaon condensate is expected. We try to give a unified view about the change of the matter structure as density increases, carefully taking into account the Coulomb screening effects from the viewpoint of first‐order phase transition. © 2004 American Institute of Physics