In early pregnancy, placental trophoblast cells rapidly grow and invade into maternal uterine tissue. N-Acetylglucosaminyltransferase V (GnT-V) and its product, beta 1-6-GlcNAc branching glycan, are known to correlate with tumor invasion and metastasis. Since the placentation process resembles invasion of cancer cells, we examined the expression of beta 1-6-GlcNAc branching glycan and GnT-V in human placenta. Placentas derived from the first trimester contained a larger amount of beta 1-6-GlcNAc branching glycan, detected by leukoagglutinating phytohemagglutinin lectin blotting, than those at term. Immunohistochemical study revealed that beta 1-6-GlcNAc branching glycans and GnT-V protein were localized in the trophoblast layer. Both protein expression and the enzyme activity of GnT-V in first trimester placentas were higher than those at term. These results suggest that GnT-V would contribute to placentation in the early phase of pregnancy, possibly regulating the process of invasion of trophoblast cells. (c) 2005 Elsevier Inc. All rights reserved.