There is provided a method for manufacturing inexpensive, highly safe, highly stable, versatile polymethoxyflavones that can be used in food products and easily incorporated into a variety of pharmaceutical formulations, whereby in one pass, a large quantity of polymethoxyflavones can be isolated from other components in citrus peel oil, as well as a method for its use. The method for manufacturing polymethoxyflavones from citrus plant peel oil comprises a step of removing the volatile components in citrus plant peel oil by distillation to obtain a distillation residue, a step of distilling the residue with a thin-film vacuum distillation apparatus to obtain a fraction, a step of extracting the fraction with an aqueous ethanol solution to obtain an extract, and a step of contacting active carbon with the extract after removal of the insoluble oils in the extract for refining, as a method for manufacturing polymethoxyflavones that are highly stable over time and have reduced residual pesticide levels.