The ultrastructures of natural and synthetic linear polymers solidified from their solutions or melts were investigated by means of electron microscopy and electron micro- and X-ray small-angle-diffraction techniques. The states of organization of micellar units in their fibril, membrane, and so-called “spherulite” were clarified. Some of the results are as follows: 1. Cellulose assembles into micell strings having the “long period” which shows a distribution and shifts to shorter length by degradation. The lateral orders between the “long periods” of neighboring strings are uneven. 2. Nylon (6) gives “spherulites” constructed with micell strings when they are crystalized in ß-form (monoclinic). The “long periods” or micell lengths vary due to the changes of crystal forms on heating and cooling. 3. Polyethylene and polyethylene terephthalate show “spherulites” having fanlike assemblies of thin laminae of mono-micellar net-works on which b and c axes lie. By stretching, the laminae are transformed into fibrils, and on heating the reverse happens. The proposed coiled ribbon arrangements of micell strings are not likely to exist. 4. Silk fibroin has two states of assembly, one involves striated lamellar structure corresponding to “pleated sheet”, and the other spiral filaments indicating the existence of “α-helix” of the molecule. 5. Polyacrylonitrile forms a texture of beaded strings whereas polyacrylamide gives a network of straight fibrils.