Mitochondria are important intracellular organelles in which energy is generated. Mitochondrial permeability transition pore (PTP) opening will induce mitochondrial dysfunction, then result in cell death. The study was caried out to investigate the influence of green tea polyphenols (GTPs) and five kinds of catechins on mitochondrial PTP opening. The results showed that GTPs and catechins have obvious and different effects on H₂O₂-induced mitochondrial PTP opening. GTPs and its major components EGCG, ECG have inhibitory effects on it, while other kinds of catechins, EGC, EC and (+)-C can accelerate the process. The data provide an alternate interpretation of the potent protective function of GTPs, EGCG and ECG.