Objective To study the significance of leptin and its receptor(OB-R) in the occurrence and development of pulmonary arterial hypertension(PAH) induced by monocrotaline(MCT).Methods Fifteen SD rats were divided into the control group(n=5) and two experimental groups(n=10).The experimental groups were intraperitoneally injected by MCT for constructing the PAH model and the control group was injected by the same dose of solvent groups.The venous blood was extracted at 2,4 weeks after MCT injection in the two experimental groups.The mean pulmonary artery pressure(mPAP) and right ventricular hypertrophy index(RVHI) were measured and then the lung tissue was removed.The pathological change of lung blood vessels was observed.The expression of serum leptin was detected by ELISA.The expression of OB-R in lung tissue was tested by Western blot.Results Compared with the control group,mPAP and RVHI in the experimental groups were significantly increased(P＜0.05);the expression levels of serum leptin and lung tissue OB-R were increased significantly(P＜0.05),moreover,which were positively correlated with mPAP(r=0.912,P＜0.05;r=0.861,P＜0.05).Conclusion Leptin and OB-R may play an important role in the occurrence and development of PAH induced by MCT.