Sex and gender differences in the clinical manifestation and outcomes of human diseases are being continuously discerned. Although gonadal hormones contribute to sex and gender differences, the effects of sexual dimorphisms at the cellular level has been acknowledged in recent years. Human umbilical vein endothelial cells (HUVECs) from twin pairs of the opposite sex represent a valuable tool to study sex-specific dimorphisms for the pathogenesis of cardiovascular diseases at the cellular level. We analyzed sexual dimorphisms on secreted proteins after different time points of serum starvation. HUVECs were serum starved for 5 and 16 hours respectively, and proteins in the cell culture supernatants were analyzed by MS/MS proteomics. Altogether, nearly 1000 secreted proteins could be detected. Long term (16 hours) compared to short term (5 hours) starvation resulted in a significant change in the level of almost 500 proteins. The majority of these proteins showed either increased or reduced levels in both sexes. Only 15 proteins exhibited significant sex-specific regulation between long versus short term starvation. However, 55 extracellular proteins showed significant sexual dimorphisms between male and female cells after the same time points of serum starvation. At both time points, a higher number of proteins were observed with higher levels in female as compared to male cells. These results demonstrate sex-specific differences between male and female cells in secreted proteins the response to serum starvation.