Three different forms of PSⅠ complexes were isolated from a siphonous marine green alga, Codium fragile, by Triton X-100 sucrose gradient centrifugation. Zone Ⅲ had a Chl a/b＞20, and designated as PSⅠ core complex CCⅠ because it created only CPⅠ band in mild PAGE. Zone Ⅳ and Ⅴ had absorption at 436 and 674 nm, 467 and 650 nm, and 540 nm, suggesting the presence of Chl a, Chl b, siphonaxanthin and siphonein, Chl a/b were 3.23 and 2.4, respectively. Both CPⅠ and CPⅠa bands were observed when they were subjected to mild PAGE. Therefore, Zone Ⅳ and Ⅴ were different forms of PSⅠ complexes that consisted of CCⅠ and different amount of light-harvesting complex LHCⅠ. Zone Ⅲ contained only 66 and 56 ku peptides in SDS-PAGE, while Zone Ⅳ and Ⅴ had 4 different LHCⅠ peptides of 25，26，26.2 and 27.5 ku in addition to 66, 56 ku peptides. Fluorescence emission spectra showed that efficient energy transfer were kept among pigments in isolated PSⅠ complexes. Excitation energy absorbed by Chl b, siphonaxanthin and siphonein can be transferred to Chl a.