Bentonite quality depends largely on its content of montmorillonite. Method of methylene blue adsoxption has been used usually to estimate the approximate montmorillonite content. But the peavey liquid separation method is considered to be the most precision process to separate the montmorillonite from other minerals. The specific gravity of alcoholic bromoform mixture, the speed and types of centrifugal equipment and other technical parameiers were studied in detail. An optimum testing procedure is described in this paper. More than 1O Chinese bentonites have been separated, and the contents of montmorillonite have been determined. A new coefficient of methylene blue adsorption for bentonite is found by comparing them with those of the methylene blue adsorption. It is considered in this paper, that this new method is important for examing the qualify of bentonite. Tlse above method is technically practical not only for fon- dry industry but also for geologic examination.