The Langmuir-Blodgett monolayers of the 10,12-tricosadiynoic acid molecules were deposited onto the basal plane of highly oriented pyrolytic graphite (HOPG) by Schaefer's method and then observed with the scanning tunnelling microscope (STM). With a view to achieving a parallel molecular arrangement on the graphite surface, the deposition was deliberately conducted at a relatively low surface pressure. As exhibited by the STM images, by this approach the 10,12-tricosadiynoic acid molecules could constitute an ordered structure with their molecular chains lying parallel to the substrate. The model of molecular dimer is put forward for the interpretation of the observed phenomena. PACS:  85. 65. +h, 07. 79. Cz