In chronic thromboembolic pulmonary hypertension (CTEPH), central thrombi are the most likely disease initiators, and progressive pulmonary vascular remodeling, which is characterized by marked proliferation of pulmonary artery smooth muscle cells (PASMCs), may also contribute to the long-term progression of CTEPH. This study was designed to investigate the cellular characteristics of PASMCs isolated from the organized thrombotic tissues of CTEPH. In the present study, analysis of PASMCs isolated from five CTEPH patients and three control subjects showed that cells from CTEPH patients had certain characteristics that distinguished them from control cells, including inferior or no cell-cell contact inhibition growth, increased sensitivity to hypoxia-induced proliferation, resistance to serum starvation-induced apoptosis, and mitochondrial metabolism disorder. These differences in the PASMCs in endarterectomized tissue of CTEPH patients may prove useful in understanding the pathobiology of CTEPH.