In biological system, various nano–assemblies are formed by self–assembly of proteins with high symmetric ternary structures. For example, dodecahedral internal skeleton of tomato bushy stunt virus is self–assembled from C₃–symmetric β–sheet subunits. Inspired by such self–assembly process, we have developed a novel strategy for construction of spherical assemblies consisting of biomacromolecules such as DNA and peptides. DNA three–way junctions bearing self–complementary sticky–ends were self–assembled into nanometer to micrometer sized spherical structures depending on the concentration. The three–way component design was extended to the design of the artificial C₃–symmetric conjugate which contains three β–sheet–forming peptides FKFEFKFE. Radial–type Trigonal–FKFE self–assembled into nanocapsules with the size of 20 nm. In contrast, wheel–type Trigonal–FKFE self–assembled into nanofibers with uniform width (3 nm). Recently, we designed T–shaped C₃–symmetric peptide conjugate Trigonal–glutathiones (TG). TG self–assembled into soft nanospheres with the size of about 100—250 nm, whose size was little affected by the concentration.