Although both tooth enamel and bone are composed of organized assemblies of carbonated apatite crystals, enamel is unusual in that it does not contain collagen nor does it remodel. Self-assembly of amelogenin protein into nanospheres has been recognized as a key factor in controlling the oriented and elongated growth of carbonated apatite crystals during dental enamel biomineralization. We report the in vitro formation of birefringent microribbon structures that were generated through the supramolecular assembly of amelogenin nanospheres. These microribbons have diffraction patterns that indicate a periodic structure of crystalline units along the long axis. The growth of apatite crystals orientated along the c axis and parallel to the long axes of the microribbons was observed in vitro. The linear arrays (chains) of nanospheres observed as intermediate states before the microribbon formation give an important indication as to the function of amelogenin in controlling the oriented growth of apatite crystals during enamel mineralization.