Abstract: The adsorption of diazepam on microcrystalline bismuth subnitrate in simulated gastric fluid at 37℃ was found to obey the Freundlich and Langmuir relationships. One g microcrystalline bismuth subnitrate was shown to be able to adsorb approximately 2～3.4 mg of diazepam in the dose from 2.5 to 5 mg. We presume that the adsorption of diazepam by microcrystalline subnitrate takes place primarily by electrostatic attraction.The possibility of desorption of diazepam from microcrystalline bismuth subnitrate was also investigated using simulated intestinal fluid and found that about 50 percent was desorped.