Aim To investigate the effects of docosahexaenoic acid （DHA） on monocrotaline-induced pulmonary hypertension （PH） in rats,and explore the potential mechanism involved in its action. Methods 24 male Sprague-Dawley rats were randomly divided into three groups: nomal control group （n7）,DHA-treated group （n7） and pulmonary hypertension model group （n10）. The monocrotaline （MCT）-induced pulmonary arterial hypertention was established.The microcosmic changes of pulmonary arterial morphologic in lung of rats were measured by optical microscope after the stain of HE. The expression of NFATc1 protein and mRNA levels in pulmonary arterial were detected by immunohistochemistry,Western blot,and qRT-PCR,respectively. Results DHA could significantly inhibit the structural remodeling of small pulmonary arterial induced by MCT. Compared with the normal group,the expressions of NFATc1 protein and mRNA were remarkably increased in MCT group. Compared with MCT group,the expressions of NFATc1 protein and mRNA were decreased significantly in DHA-treated group. Conclusions DHA reverses the development of pulmonary hypertention induced by MCT in rats. The mechanism may be related to reduction of the expression of NFATc1.