Aim To study the effects of c jun antisense gene on phenotypic switch of vascular smooth muscle cells (VSMC). Methods Eukaryotic expression vectors which could transcript into c jun antisense RNA were transfected into rat VSMC, Northern blotting, Western blotting and 3 H TdR incorporation were used to observe the effects of c jun antisense RNA on the expression of phenotypic marker genes SM α actin, SMemb, osteopontin and DNA synthesis of VSMC. Results By the c jun antisense RNA expressed in VSMC, compared with control group, the mRNA expression of dedifferentiated marker genes SMemb and osteopontin decreased 50% and 95% respectively, the osteopontin decreased 75%, and the DNA synthesis of VSMC was evidently inhibited, the 3 H TdR incorporation decreased 37%, but the effect of c jun antisense RNA on differentiated marker gene SM α actin had not been observed. Conclusion The expressive products of c jun gene was important for VSMC to keep dedifferentiated.