Phycobilisomes (PBSs) are supramolecular pigment–protein complexes composed of phycobiliproteinslinker proteins, serving as the major light-harvesting complexes that capturetransfer light energy to photosystem II (PSII)photosystem I (PSI) in cyanobacteriaeukaryotic red algae. In cyanobacteria, a rod-type PBS that does not have a core is specifically connected to PSI by a linker protein CpcL to form a PSI-CpcL-PBS supercomplex. However, the mechanism of CpcL-PBS association to PSI remains unclear. Here, we report the cryoelectron microscopic structures of PSI-CpcL-PBS at 2.98 ÅCpcL-PBS at 2.93 Å resolution from a cyanobacterium Anabaena sp. PCC 7120, respectively. CpcL-PBS is located on the stromal side of a PSI tetramerexhibits a structure of three-layered PBS consisting of four linkers (CpcL, CpcC1, CpcC2, PecC)18 pairs of phycocyanin αβ monomers. The C-terminal transmembrane helix of CpcL inserts to the membraneinteracts with PsaA, PsaB,PsaM of PSI at an interface I between two PSI monomers, enabling the formation of the PSI-CpcL-PBS supercomplex. The exact structure of protein subunitsarrangement of bilinchlorophyll pigments are revealed, which provide a structural basis for the assembly of PSI-CpcL-PBSpossible excitation energy transfer pathways from antennas to PSI within this supercomplex, shedding light on the organizationattachment of CpcL-PBS in cyanobacterial thylakoids.