Objective:To explore the activity of Nacetylglucosaminyltransferase Ⅴ（GnTⅤ） in breast cancer tissues and to discuss its clinical significance.Methods:The activities of GnTⅤwere examined in a tissue microarray cohort of 57 breast carcinomas and 12 benign breast lesions.Lectin blotting using Phaseolus vulgaris leukocytic phytohemagglutinin (PHAL) labeling was used to assay GnTⅤactivity.The relationship between clinicopathological parameters and GnTⅤactivity was investigated.Results:High activity of GnTⅤwas observed in 89.47% (51/57) breast cancer tissues,which was significantly higher than that in the benign breast lesions (8.33％\[1/12\],P<0.01).No difference in GnTⅤactivities was observed in breast cancer patients with different pathological types,different lymphatic statuses,and different stages.Conclusion:Higher GnTⅤactivity in breast cancer tissues indicates a higher risk of malignancy.Targeting GnTⅤmight be a future way for treatment of triplenegative breast cancer patients with recurrence and metastasis.