This study aims to investigate the roles of Adipose-Derived Stem Cells (ADSCs) transplantation in treating Monocrotaline (MCT) induced Pulmonary Arterial Hypertension (PAH). The adipose cells were obtained by collagenase digestion and the PAH model was obtained by intraperitoneal injection of MCT (50 mg/kg). On day 14, group ADSCs was injected with ADSCs, and the mean pulmonary artery pressure (mPAP), percentage of wall thickness to vascular diameter (WT%) and percentage of wall area to total vascular area (WA%) of tunica media in small artery, Right Ventricular Hypertrophy Index (RVHI%) and other indicators were detected. Results showed that, ADSCs were successfully cultured, and the MCT-induced PAH model was successfully established. After ADSCs transplantation, group ADSCs significantly improved mPAP and corresponding pulmonary pathological indicators than the group PAH. ADSCs significantly attenuated PAH as assessed by reductions in mPAP (32.5 ± 4.2 vs. 57.8 ± 4.4, P<0.01), the RVHI% (0.30 ± 0.01 vs. 0.40 ± 0.01, P<0.01), WT% (38.89 ± 2.12 vs. 49.62 ± 2.92, P<0.01) and WA% (54.73 ± 1.80 vs. 66.92 ± 2.86, P<0.01), the degree of non-muscular pulmonary arterial muscularization (0.32 ± 0.04 vs. 0.55 ± 0.07, P<0.01), infiltration of inflammatory cells around the small pulmonary arteries (2.52 ± 0.17 vs. 3.71 ± 0.20, P<0.01). ADSCs transplantation can reduce mPAP and pulmonary vascular pathological changes, and may have therapeutic effects on PAH.