Abstract: A technique for separating the pigment-protein complexes from brown algae Undaria pinnatifida had some improvement in this work. Pigment-protein complexes were isolated by centrifugation on discontinuous sucrose density gradient of the SDS-treated thylakoid membranes. The best separation was obtained with detergent SDS (SDS:Chl=20:1, solubilized 20 min at 4℃), and sucrose density gradients (10%,15%,20%,30%,40%,50%,60% W/W). The 40% sucrose layer represented photosystemⅠ (PSⅠ) complex. In contrast with red algae, the results suggested that PSⅠ complex from Undaria pinnatifida had no symbol of 730 nm fluorescence peak.