The adsorption and assembling of bacteriochlorophyll c (BChl c) on a highly oriented pyrolytic graphite (HOPG) surface have been investigated by the scanning tunneling microscopy (STM). BChl c molecules are found to self-organize a well-defined adlayer on HOPG surface with a monomeric structure different fromthe dimer association seen on adlayers of Chls a, c and BChlide c, d. A structural model is proposed for the adlayer.