Recent interest in green tea polyphenols has increased owing to their antioxidant activities and their possible role in the prevention of cancer and cardiovascular diseases. Typically, 93% compounds of total polyphenols in green tea leaves, many of which are called catechins, are flavonoids. The major tea catechins are a mixture of epicatechin isomers, including (-)-epigallocatechin gallate (EGCG), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), and (-)-epicatechin (EC). Separation of green tea catechins is generally carried out by HPLC-UVD. UV detector is a suitable detector for quantification this class of molecules and allows high sensitivity level for polyunsaturated species. However, UV detection does not discriminate different compounds having similar chromophore groups. More detailed structural information can be collected when a mass spectrometer is coupled with a UV-DAD. MSD is a powerful tool for qualitative analysis to identify and confirm molecular structures of unknown compounds, and it is particularly useful for quantitative analysis, owing to its high sensitivity and selectivity. This study describes the application of HPLC-DAD/MS methods for the rapid and routine analysis of 9 catechins in green tea leaves. Green tea extracts were injected directly onto a reversed phase HPLC column. Compounds, identified on the basis of their absorbance and MS spectrum, included gallic acid, (-)-epicatechin, and their various gallate derivatives. HPLC/MS detection was found to be more sensitive than UV-DAD, and MSD showed good precisions for quantification of catechins.