Abstract: Methylsulfonylmethane (MSM) is naturally accruing organic sulphur that is known as a potent anti-inflammatory compound. The aim of this study was to investigate the effect of MSM on mRNA expressions of angiotensinogen, endothelin-1 (ET-1) and Transforming Growth Factor (TGF)-β1 in rats with monocrotaline (MCT)-induced pulmonary arterial hypertension. Wistar rats were randomly assigned to 38-days pretreatment or 28-days treatment. MSM was administered to either 10 days before or 14 days after a single dose of MCT. Right Ventricle (RV) tissue samples were obtained to evaluate changes in the inflammatory genes expression using RT-PCR assay. The expression levels of angiotensinogen, ET-1 and TGF-β1 significantly were reduced (p<0.01) at efficient dose of MSM in MCT-induced pulmonary arterial hypertensive rats. Results suggest that harmful effects of MCT induced PAH on the RV function could be attenuated by anti-inflammatory actions through the suppression of local RAAS along with associated growth-promoting factors TGF-β1 and ET-1.