Liquid chromatography combined with multiple-stage mass spectrometry (LC/MSn) was used to study the pathway of the release of gallic acid (GA) from epigallocatechin gallate (EGCG) in infusion of old oolong tea. The possibility of releasing GA from EGCG in old tea preparations was supported by an in vitro observation of GA degraded from EGCG under heating conditions mimicking the drying process. Negative electrospray ionization with the data-dependent mode of MSn was used to study the formation pathway of GA in old oolong tea. The MSn data show that GA was released from the dimer of EGCG, not directly degraded from EGCG. Copyright © 2010 John Wiley & Sons, Ltd.