2,4,6-Tris(1,3-dithiol-2-ylidene)-1,3,5-cyclohexanetrione (C 15 H 6 O 3 S 6, abbreviated TDTCHTO) has a shape of triangular propeller-like structure, and is known to crystallize as an orthorhombic structure (orthorhombic-I) by solution-growth process. In this study, monolayer of TDTCHTO was grown on a graphite (0 0 1) surface by vacuum-deposition, and was studied on its structure and epitaxy by STM. The observed two-dimensional lattice of TDTCHTO monolayer is hexagonal with a=1.77 nm, in which the two molecules stack with their triangular molecular planes parallel onto the graphite surface. As a result, the monolayer of TDTCHTO forms a different layer structure from the known orthorhombic structure, and therefore the molecular packing with hexagonal symmetry may be promoted by the symmetry of graphite surface. From the STM observation, the epitaxy is concluded as commensurate, not point-on-line coincidence, which means that an interaction between TDTCHTO and graphite is stronger comparing with side-by-side intermolecular interaction in the monolayer. The a-axis of the monolayer TDTCHTO makes an angle of 14° with the a-axis of graphite, and every molecule is coordinated on equivalent lattice point of graphite. This monolayer structure is discussed in relation with the orthorhombic-II observed with TEM for a thicker film grown on graphite.