We purified and characterized a bovine pregnancy-associated protein in pregnant cow urine using two-dimensional gel electrophoresis. Urine from cows was collected according to their status of pregnancy and non-pregnancy. Proteins in the cow urine were fractionated with 50% ammonium sulfate prior to two-dimensional gel electrophoresis. Proteins separated on the gels were compared in terms of expression level and new expression by molecular mass and isoelectric point. We localized two pregnancy-associated protein spots on the gels at molecular masses of 24 kDa and 20 kDa and isoelectric points of 5.5 and 5.7, respectively. Likewise, two non-pregnancy specific proteins were localized at 27 kDa and 28 kDa with isoelectric points of 5.7 and 5.9, respectively. To rule out the possibility that environmental or genetic factors might influence the expression of the proteins, we demonstrated the pregnancy-associated expression of the proteins in two-dimensional gels with pregnant urine taken from cows raised in a different institute. The pregnancy-associated protein with molecular mass of 20 kDa and isoelectric point of 5.7, namely spot 2, was microsequenced and found to be highly homologous to the bovine collagen alpha 1 chain.