A stable concentrated dietary supplement containing fucoxanthin as the main active component. The dietary supplement is made by a process including grinding crude freeze-dried flakes of wakame seaweed (Undaria pinnatifida) with desirable characteristics into a powder, extracting the active fucoxanthin from the powder with use of an aliphatic or aromatic organic solvent, then filtering and distilling the extract to form a thick syrupy fucoxanthin-containing mass having a solids content of from about 10-99% by wt. The mass is then purified by dissolving it in an organic non-polar solvent having a Polarity Index of