Objective    To investigate the protective effect and mechanism of Baicalin on monocrotaline-induced pulmonary hypertension in rats.    Methods   Forty SD rats were randomly divided into 4 groups: a control group, a pulmonary hypertension group, a baicalin 50 mg·kg-1 group and a baicalin 100 mg·kg-1 group. A single intraperitoneal injection of  monocrotaline (60mg/kg) was used to establish the pulmonary hypertension model. After injection of  monocrotaline, baicalin was gavage continuously for 28 days. Right ventricular catheterization method was used to detect RVSP and mPAP. The levels of SOD, GSH-px, ICAM-1, VCAM-1, IL-8 and IL-1β in serum were detected by ELISA. The formation of reactive oxygen species (ROS) in lung tissue was observed by DHE staining. The expression of bax and bcl-2 in lung tissue were detected by immunofluorescence. Western blot was used to detect the protein expression of PDGF and P38 MAPK.   Results   Compared with the model group, mPAP, RVSP, RVHI and W/D were significantly decreased, and the contents of ICAM-1, VCAM-1, IL-8 and IL-1β in serum were significantly decreased, the contents of bcl-2, SOD and GSH-px were increased significantly in the Baicalin group. The contents of ROS, bax, PDGF and P38 MAPK and the level of bax/bcl-2 ratio in lung tissue were significantly decreased in the Baicalin group.    Conclusions   Baicalin may play a protective role in improving inflammation, oxidative stress and apoptosis of rats with pulmonary hypertension through PDGF/P38 MAPK signaling pathway.