Lanthanide bisphthalocyanine complexes are interesting objects for the construction of two-dimensional (2D) ordered arrays with prospective applications in molecular electronics due to their unique semiconductor and electrochromic properties as well as their double-decker architecture. The 2D self-assembly of dodecyloxy-substituted (bisphthalocyaninato)erbium(III) has been studied at the solid (highly oriented pyrolytic graphite)-liquid interface by scanning tunneling microscopy. The results show that the bisphthalocyanine molecules form an ordered quadratic 2D lattice (alpha = b = 3.0 +/- 0.+/- 1 nm, gamma = 3 degrees), which is nearly identical to that formed by its (phthalocyaninato)cobalt(II) analogue bearing alkoxy chains of the same length. This clearly shows that sandwich molecules adsorb to the graphite surface by one of the phthalocyanine disks and its eight alkoxy groups. Despite the very similar mode of interaction with the surface, mixtures of alkoxylated (bisphthalocyaninato)erbium(III) with its (phthalocyaninato)cobalt(II)analogueshow partial phase separation on the nanoscale: areas are enriched in one of the compounds. A much clearer phase separation between (bisphthalocyaninato)erbium(III) and (phthalocyaninato)cobalt(II) molecules was achieved by mixing molecules containing alkoxy groups of different length. The results provide insight for the development of well-ordered nanostructures of bisphthalocyanines in the presence of phthalocyanines, which could be of importance for future nanometer-scale functional materials.