Abstract: Objective: To study the effect of TanshinoneⅡA (TSN) on vascular smooth muscle cells (VSMCs) induced by high glucose and its relationship with MAPK signal pathway. Methods: After the establishment of the model of diabetic rats, the aortic of rats was separated carefully to culture VSMCs with the method of explant culture. DNA synthesis was analyzed by ELISA of BrdU. The activity of MAPK was measured by liquid scintillation counting. Result: It was shown that TSN inhibited the proliferation and DNA synthesis of vascular smooth muscle cells from diabetic rats in dose-dependent manner. TSN at the dose of 0.5μg·ml-1 significantly decreased the activity of MAPK, as well as of U0126. Conclusion: The effect of TSN on the proliferation and DNA synthesis of vascular smooth muscle cells from diabetic rats might be due to the inhibition of MAPK.