Aim To observe the apoptosis in endothelial outgrowth cells (EOC) induced by asymmetric dimethylarginine (ADMA) and the relevant signal transduction pathway by detecting the activity of caspase-3. Methods EOC were isolated from umbilical cord blood and then cultured. The endothelial characteristic of the cells were identified by DiI-ac-LDL and FITC-UEA-Ⅰ double fluorescent staining. Take the 0 μmol/L ADMA group as the control group. The adherent cells were treated with different concentrations of ADMA (0,1,5,10,30 μmol/L) for 48 h,then the morphological changes of cells was observed by the laser scanning confocalmicroscope. The adherent cells were treated with different concentrations of ADMA for 48 h or with ADMA(10 μmol/L)for various periods (3,6,9 h),then caspase-3 activity was measured by Microplate Reader. The adherent cells were pretreated for 30 min with ac-DEVD-CHO (100 μmol/L)-caspase-3 specific inhibitor,then 10 μmol/L ADMA was added and incubated for 48 hours. The apoptotic rate of EOC of all the groups was measured by Annexin V-FITC and Propidium iodide(PI) double staining flow cytometry. Results Typical apoptotic morphological changes can be seen in EOC after treatment of ADMA and the apoptotic rate of EOC rised accompanying with the increase of the concentration of ADMA. The activity of caspase-3 was enhanced in a dose and time dependent manner during this process. Its specific inhibitor ac-DEVD-CHO can attenuate the apoptosis induced by ADMA. Conclusion ADMA can induce apoptosis in EOC in a dose-dependent manner. This effect may be achieved by activating the intrinsic apoptoctic pathway-caspase-3 signal transduction pathway.