The two-dimensional assemblies of truxenone, diindeno[1,2-a;1',2'-c]fluorene-5,10,15-trione, on the Au(111) surface have been studied by scanning tunnelling microscopy in ultrahigh vacuum. It is found that the truxenone monolayer on Au(111) exhibits different two-dimensional supramolecular structures. The investigation using scanning tunnelling microscopy combined with the density functional theory calculations can be a helpful approach to understand the complicated supramolecular structures of truxenone self-assembly on Au(111).