A procedure for herbal extraction has been developed for producing a Chinese herbal medicine (CHM) with consistent quality regardless of the source of the herb. The quality assurance (QA) procedure is based on a model which accounts for the physicochemical phenomena governing herbal extraction. With this model and the companion experiments for determining the relevant model parameters, the amount of each herb needed from different herb quality classes to produce a CHM decoction with consistent quality can be determined. The procedure was illustrated by the extraction of Danshen and that of Gegen. For both examples, the experimental chemical marker concentrations fell within +/- 10% of the specified concentrations by using the amount of herb from each herb class as predicted. (c) 2013 American Institute of Chemical Engineers AIChE J, 59: 4241-4254, 2013