Aim To investigate the mitogenic effect of urotensin II on cells. Methods In cultured rat aorta smooth muscle cells (VSMC), tracheal smooth muscle cells (TSMC), cardiac fibroblasts (CF) and glomerular mesagial cells (GMC), UⅡ was used to stimulate these cells and levels of 3 H-TdR incorporation were used to evaluate the speed of DNA synthesis. Results UⅡ increased levels in concentration-dependent manner of 3 H-TdR incorporation of these cells significantly. But in different cells, UⅡ of same concentration did not induce same effect. 10 -10 mol/L UⅡ could increase levels of 3 H-TdR incorporation of CF and TSMC only, with the incorporation of CF higher than TSMC, while 10 -9 ～10 -8 mol/L UⅡ induced effect in the following order:CF>TSMC>GMC>VSMC. However, 10 -6 ～10 -7 mol/L UⅡ showed weaker stimulating effects on CF than lower concentration of UⅡ(10 -10 ～10 -8 mol/L). Conclusion These study provides evidence that urotensin II is an endogenous mitogen for some cells and the contribution of mitogenic effect of UⅡ to diseases deserves investigating greatly.