Pulmonary hypertension (PH) mainly results from excessive proliferation of pulmonary artery smooth muscle cells (PASMCs) and displays mitochondrial abnormalities such as mitochondrial fragmentation. Epigallocatechin-3-gallate (EGCG), an efficient antiproliferative compound in green tea, has recently been demonstrated to inhibit PASMCs proliferation. However, the pre-clinical issues as to whether EGCG attenuates PH and the underlying mechanisms have yet to be addressed. The present study was undertaken to investigate the therapeutic effects of EGCG on PH and its effects on mitochondrial fragmentation in PASMCs. Rats exposed to hypoxia (10% O2, 3 weeks) developed PH. EGCG (50, 100 or 200 mg/kg/d, i.g.) dose-dependently attenuated right ventricular systolic pressure, pulmonary vascular remodeling and right ventricular hypertrophy, increased expression of mitochondrial fusion protein - mitofusin-2 (MFN-2), and promoted mitochondrial fusion as evidenced by decreased number and volume of mitochondria in PASMCs of pulmonary arteries. Notably, EGCG (50 μM) downregulated hypoxia-induced (3% O2, 48 h) PASMCs mitochondrial fragmentation and inhibited PASMCs proliferation via KLF-4/MFN-2/p-Erk signaling pathway. Collectively, our data demonstrated that EGCG exerts antiproliferative effects via regulating mitochondrial fragmentation of PASMCs and EGCG holds the promise as a drug against PH.