The antiproliferative effect of a carotenoid-containing extract from the brown algae, Costaria costata (Sujime) and Alaria praelonga (Ainu-wakame) was investigated using cultured cancer cells. The carotenoids of 'Sujime' and 'Ainu-wakame' were mainly composed of fucoxanthin. The carotenoid fraction suppressed cell growth in HL-60 cells considerably in a dose-dependent manner, but only slightly in MKN-45 cells. Furthermore, these fractions suppressed cell growth in WI-38 VA13 cells that transformed fibroblast WI-38 cells, considerably in a dose-dependent manner, but not in WI-38 cells. These results suggest that the carotenoid fraction containing mainly fucoxanthin from 'sujime' and 'Ainu-wakame' has selective antiproliferative properties.