Angiotensin Ⅱ (AngⅡ) can induce the expression of its precursor, angiotensinogen, in vascular smooth muscle cells (VSMC), which is related with increased activating protein-1 (AP-1) binding to its cis-element located in the angiotensinogen gene promoter. In the present study, cycloheximide (CHX) was used as an inhibitor to interrupt c-Jun, the role of AP-1 in AngⅡ-induced its precursor gene activation was investigated by DNA-protein interaction and immunoblotting. The results showed that the level of c-Jun, the component of transcription factor AP-1, was significantly increased in the nucleus of VSMC after AngⅡ treatment. The majority of c-Jun was found in the nucleus but hardly detected in the cytoplasm by immunocytochemistry staining. Immunoprecipitation assays confirmed that AngⅡ could induce serine phosphorylation of c-Jun. EMSA results indicated that the level of phosphorylated of c-Jun had a positive correlation with AP-1 binding activity to cis-acting element of angiotensinogen gene and transcription activation of angiotensinogen. CHX inhibited AngⅡ- induced binding activity of AP-1 by reducing the phosphorylation of c-Jun, though it did not affect the expression of c-Jun. These findings suggest that the AP-1 phosphorylation induced by AngⅡ is one of the important mechanisms whereby AngⅡ regulates its precursor gene expression in feedback manner. It is found that CHX is an inhibitor to phosphorylation of c-Jun.