Adrenal gland is a crucial endocrine gland, and the most important function is to synthesize and secrete catecholamines (CATs) which play crucial roles in balancing homeostasis and the responding to stress. microRNA-375 (miR-375) has been detected to highly express in the adrenal, however its role and underlying mechanism are currently unclear. Herein, our results showed that miR-375 was specifically localized to the rat adrenal medulla chromaffin cells, and miR-375 expressing level decreased, when the rats were exposed to stress. The further functional studies demonstrated that the inhibition of endogenous miR-375 induced the secretion of CATs in primary rat medulla chromaffin cells and in PC12 cells, and over-expression of miR-375 resulted in decline of the CATs secretion. Furthermore, the results showed that miR-375 negatively regulated tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) and mediated adrenomedullary CATs biosynthesis. Sp1(a transcriptional activator of TH and DBH) was involved in mediating the regulation of TH and DBH as miR-375 direct target gene. These novel findings suggest that miR-375 acts as a potent negative mediator in regulating the synthesis and secretion of CATs in the adrenal medulla during the maintenance of homeostasis under stress.