Zinc-chlorin 3 (see Fig. 2 in text) possessing a tertiary 3¹-hydroxyl group and a 13-keto group was synthesized as a model for the antenna chlorophylls of green bacteria. Self-aggregation of 3 in nonpolar organic media was examined and compared to 1 and 2 possessing a primary and secondary 3¹-hydroxyl group, respectively. Zinc-chlorin 3 self-aggregated in 1 vol% CH₂Cl₂–hexane to form oligomers and showed a red-shifted Q_y maximum at 704 nm compared to the monomer (648 nm in CH₂Cl₂). This red-shift is larger than that of 2S (648 → 697 nm) and comparable to that of 2R (648 → 705 nm), but smaller than that of 1 (648 → 740 nm), indicating that while a single 3¹-methyl group (prim-OH → sec-OH) suppressed close and/or higher aggregation, the additional 3¹-methyl group (sec-OH → tert-OH) did not further suppress aggregation. The relative stability of the aggregates was in the order 1 > 2R ∼ 3 > 2S as determined by visible spectral analyses. Molecular modeling calculations on dodecamers of zinc-chlorins 1, 2R and 3 gave similar well-ordered energy-minimized structures, while 1 stacked more tightly than 2R and 3. In contrast, 2S gave a relatively disordered (twisted) structure. The calculated dodecameric structures could explain the visible spectral data of 1–3 in nonpolar organic media.