Down sydrome (DS) is a relatively frequent chromosomal disorder, which has no safe and effective method of prenatal diagnosis to date. The present study was designed to identify DS biomarkers. We quantified the changes in the umbilical cord blood protein levels between DS-affected and healthy (control) pregnant females using isobaric tags for relative and absolute quantification (iTRAQ) and Gene Ontology (GO) analysis. A total of 505 proteins were identified, and of these, five proteins showed significantly different concentrations between the DS and the control group. These proteins may thus be relevant to DS and constitute potential DS biomarkers.