Aim To discuss the regulation of expression of GATA-6 by nitric oxide/cGMP-dependent protein kinase I in vascular smooth muscle cells(VSMC) phenotypic modulation. Methods Cultured wistar rat aortic VSMC were used as an experimental model.Cell growth was determined by MTT assay.The mRNA and protein expression of GATA-6 and smooth muscle myosin heavy chain(sm-MHC) were assayed by RTPCR and Western blot analysis. Results The results showed that phenylephrineinduced proliferation of VSMC was inhibited by S-nitroso-N-Acetylpenicillamine (SNAP) and Sp-8-pCPT-cGMPs,but promoted by Rp-8-pCPT-cGMPs.The expression of GATA-6 and sm-MHC mRNA and protein were increased by SNAP and Sp-8-pCPT-cGMPs,and decreased by Rp-8-pCPT-cGMPs. Conclusions NO/PKG I can up-regulate the expression of GATA-6 and sm-MHC at the transcriptional and translational level.These findings demonstrate that NO/PKG I pathway is involved in the maintenance of the differentiated phenotype in VSMC.