Remarkably strong binding of berberine to 4-sulfonatocalix[8]arene was found in aqueous solution, which led to fluorescence quantum yield increase of a factor about 40 at pH 2. The hypsochromic shift of the fluorescence maximum implied that berberine sensed less polar microenvironment when confined to SCX8. The stability of the supramolecular complex significantly diminished when sulfocalixarenes of smaller ring size served as host compounds but the pH affected the association strength to a much lesser extent. All berberine complexes proved to be barely fluorescent at pH 12.2 because of excited state quenching by the hosts via electron transfer. (c) 2006 Elsevier B.V. All rights reserved.