When the light-harvesting chlorophyll a/b protein complex (LHC-II) from pea thylakoid membranes is co-crystallized with native lipids, an octahedral crystal that exhibits no birefringence is obtained. Cryogenic electron micrographs of a crystal edge showed the crystal to be made up of hollow spherical assemblies with a diameter of 250 A. X-ray diffraction data at 9.5 A resolution revealed the spherical shell of LHC-II to have icosahedral symmetry. A T = 1 icosahedral model of LHC-II, in which the stromal surface of the protein faces outward, was constructed using the previously reported structure of the LHC-II trimer [Kühlbrandt et al. (1994), Nature (London), 367, 614-621]. The present result shows the first example of a well ordered three-dimensional crystal of icosahedral proteoliposomes.