We prepared self‐aggregative bacteriochlorin (1) by modifying naturally occurring bacteriochlorophyll‐a. These synthetic 31‐epimers were separated and the absolute configuration at the 31‐position was determined. Epimerically pure 31R‐ and 31S‐1were mildly oxidized to afford the corresponding chlorins, 31R‐ and 31S‐2, respectively. A dichloromethane solution of 31R‐ or 31S‐1was diluted with 1000 fold volume of cyclohexane to give self‐aggregation species absorbing lights at a near‐infrared region (< 910 nm). The resulting Qymaximum in 31R‐1was 860 nm and red‐shifted by 2170 cm−1from the monomeric one, whereas epimeric 31S‐1showed a less red‐shifted peak at 798 nm. In contrast, self‐aggregation of 7,8‐dehydro‐compound2showed much smaller diastereomeric control. Such visible spectra indicated that the self‐aggregates of 31R‐1gave different supramolecular structures from those of 31S‐1. Molecular modeling calculation suggested that 31R‐1self‐aggregated in the same manner as 31R‐2did to give large oligomer but 31S‐1self‐aggregated in a less‐ordered orientation than 31S‐2did. © 2004 American Institute of Physics