A new type of decagonal phase having superlattice order has been found in an AI70Ni15Co15alloy by means of the electron diffraction technique. Most of the grains in the Al70Ni15Co15sample heat treated at 600°C for 216h exhibit superlattice order. In contrast, superlattice order has not been seen for the Al65Cu20Co15decagonal phase. The relation between the structures with and without superlattice order is discussed using a four-dimensional description of the decagonal quasicrystalline structure.