The apoptosis-inducing effect of fucoxanthin on human leukemic HL-60 cells was investigated. Fucoxanthin, which was obtained from the brown alga Undaria pinnatifida, inhibited the proliferation of HL-60 cells and induced DNA fragmentation on agarose gel electrophoresis, a typical characteristic feature of apoptotic cells. The results of sandwich ELISA using anti-biotin-antibody and anti-DNA-antibody also demonstrated DNA fragmentation in accordance with the increase in fucoxanthin concentration and incubation time. Since the level of DNA fragmentation did not increase after 24 h incubation, fucoxanthin appeared to have some effect on cell cycle. In contrast, β-carotene did not show an apoptosis-inducing effect on HL-60 cells. These results suggested that a carotenoid structure might be crucial for inducing apoptosis.