Abstract: Fluorescence emission spectra of brown algae Undaria pinnatifida, Dictyopteris divaricata, Laminaria japonica, Colpomenia sinuosa, Sargassum confusum, Sargassum thunbergii, Scytosiphon lomentarius and Ectocarpus confervoides were determined and compared to the higher plant Spinacia oleracea and red alga Porphyra yezoensis at 77 K. The results showed that brown algae were significantly different from higher plant and red alga, they had no fluorescence emission at 730 nm which is taken as the characteristic of PSI. The spectra were divided into two types according to the wavelength of major fluorescence emission. It was at 690 nm in Undaria pinnatifida, Dictyopteris divaricata, Laminaria japonica, Colpomenia sinuosa and at 705 ～ 720 nm in Sargassum confusum, Sargassum thunbergii, Scytosiphon lomentarius, Ectocarpus confervoides. The characterization of fluorescence at 77 K may foresee the difference of PSI structure between brown algae and higher plant.