In the present study, black soybeans were fermented with Aspergillus awamori at 30 degrees C for 3 days. The effect of fermentation on the antiproliferative effect against human colon cancer cells, Caco-2 and HT-29 as well as Cu2+-chelating effect of black soybeans was investigated. It was found that the water, 80% methanol or 80% ethanol extract of fermented black soybeans showed a significantly higher (P < 0.05) antiproliferative and Cu2+-chelating effect than did the respective extract of non-fermented black soybeans. Generally, the methanol extract and the ethanol extract of fermented black soybeans exerted higher antiproliferative effect on both Caco-2 and HT-29 cells. While water extract of fermented black soybeans showed the highest Cu2+-chelating effect among the various extracts examined. Taking into account of extraction yields further revealed that bioactive principles that exhibit Cu2+-chelating effect could be extracted to the largest extent with water as the extraction solvent. With same amount of sample, water extract obtained from fermented black soybeans possesses the highest Cu2+-chelating abilities. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.