AbstractIntroduction – Salvianolic acid B (Sal B) is one of the major water‐soluble compounds isolated from the roots of Salvia miltiorrhiza, which is widely used as a traditional Chinese medicine. Although much research on the general stability of Sal B has been undertaken and reported, there is still a need for further study of the stability required as a potential drug material.Objective – To study the stability of Sal B in the solid state and in normal saline (NS) solution during storage, as required in the ICH guidelines (2003) and Chinese Pharmacopoeia (2005).Methodology – Sal B stability was analysed using the high‐performance liquid chromatography (HPLC) method described in the Chinese Pharmacopoeia. HPLC coupled with time‐of‐flight mass spectrometry (HPLC‐TOFMS) was applied for the separation and identification of the degradation products of Sal B.Results – In the solid state, Sal B packaged in aluminium foil bags was stable for 6 months under ‘accelerated conditions’ (40°C, 75% relative humidity, RH). However, solid Sal B degradation was observed under open exposure to stress conditions of high temperature (60°C) or high humidity (92.5 or 75% RH). In NS solution, Sal B underwent severe degradation under accelerated conditions. Through HPLC‐TOFMS, nine degradation products were identified and the possible degradation pathway was deduced.Conclusion – The results demonstrate that the potential drug material Sal B could be used in a solid formulation, but is not suitable for use as a liquid formulation. Copyright © 2011 John Wiley & Sons, Ltd.