The chlorosomal light-harvesting antennae of green phototrophic bacteria consist of large supramolecular aggregates of bacteriochlorophyll c (BChl c). The supramolecular structure of (3¹-R/S)-BChl c on highly oriented pyrolytic graphite (HOPG) and molybdenum disulfide (MoS₂) has been investigated by scanning tunneling microscopy (STM). On MoS₂, we observed single BChl c molecules, dimers or tetramers, depending on the polarity of the solvent. On HOPG, we observed extensive self-assembly of the dimers and tetramers. We propose C=O · · · H–O · · · Mg bonding networks for the observed dimer chains, in agreement with former ultraviolet–visible and infrared spectroscopic work. The BChl c moieties in the tetramers are probably linked by four C=O · · · H–O hydrogen bonds to form a circle and further stabilized by Mg · · · O–H bondings to underlying BChl c layers. The tetramers form highly ordered, distinct chains and extended two-dimensional networks. We investigated semisynthetic chlorins for comparison by STM but observed that only BChl c self-assembles to well-structured large aggregates on HOPG. The results on the synthetic chlorins support our structure proposition.