Objective To design and synthesize a series of novel dithiodipropionamide derivatives based on precursor captopril, and to investigate their vascular endothelial cell protective activities. Methods Based on the structure of captopril, we designed and synthesized five dithiodipropionamide derivatives, whose mercapto propionamide and methyl side chain were retained and the proline were modified. Human umbilical vein endothelial cells (HUVECs) were exposed to H₂O₂ at a concentration of 400 μmol/L for 3 h. Then in vitro endothelial cell protective activities of the target compounds were determined using captopril as the positive control drug. Results The target compounds were confirmed by nuclear magnetic resonance spectroscopy (¹HNMR and ¹³CNMR) and electrospray ionization-mass spectrometry (ESI-MS). Preliminary results of vascular endothelial cell protective activity test showed that, except for compound 4c, all the four target derivatives exhibited cytoprotective activity to different extents. The compound 4e, namely 3,3’-disulfide (N-(［1,1’-biphenyl］-3-methyl)-2-methylpropionamide) had the best activity. Conclusion The proline structure on captopril substituted by relatively large hydrophobic fragments, such as 4-methylbenzylamine and 4-tert-butylbenzylamine, followed by dimerization, can improve protective activity of vascular endothelial cells.