AbstractIt is known that nobiletin possesses anticancer, antiviral and anti‐inflammatory activities. Recently, the demand for nobiletin in large quantities and high purity has increased. However, conventional normal‐phase silica gel chromatography and C18‐reverse‐phase separation methods cannot satisfy the requirement of pure and gram scale nobiletin in a timely manner. In exploring the composition and the biological activities of polymethoxyflavones from sweet orange (Citrus sinensis) peel, we developed an efficient isolation method for nobiletin. By employing this methodology, pure nobiletin, in gram quantities, was obtained in only one purification cycle. The orange peel extract was loaded onto a silica gel flash column and eluted by a mixed solvent system of ethyl acetate and hexanes, and the fractions collected. Upon combination of the eluted fractions, mainly containing nobiletin and 5,6,7,4′‐tetramethoxyflavone, and concentration under reduced pressure, the resultant residue was loaded onto a Regis chiral column. Gram amounts of nobiletin and 5,6,7,4′‐tetramethoxyflavone were then eluted with ethanol and hexanes, respectively. Copyright © 2005 John Wiley & Sons, Ltd.