Drug resistance is a major problem in cancer chemotherapy. Aberrant glycosylation has been known to be associated with cancer chemoresistance. Aim of this work is to investigate the alterations of glycogene and N-glycan involved in multidrug resistance (MDR) in human breast cancer cell lines. Using real-time polymerase chain reaction (PCR) for quantification of glycogenes, fluorescein isothiocyanate (FITC)-lectin binding for glycan profiling, and mass spectrometry for N-glycan composition, the expression of glycogenes, glycan profiling, and N-glycan composition differed between drug-resistant MCF/ADR cells and the parental MCF-7 line. Further analysis of the N-glycan regulation by tunicamycin (TM) application or PNGase F treatment in MCF/ADR cells showed partial inhibition of the N-glycan biosynthesis and increased sensitivity to chemotherapeutic drugs dramatically both in vitro and in vivo. Using an RNA interference strategy, we showed that the downregulation of MGAT5 in MCF/ADR cells could enhance the chemosensitivity to antitumor drugs both in vitro and in vivo. Conversely, a stable high expression of MGAT5 in MCF-7 cells could increase resistance to chemotherapeutic drugs both in vitro and in vivo. In conclusion, the alterations of glycogene and N-glycan in human breast cancer cells correlate with tumor sensitivity to chemotherapeutic drug and have significant implications for the development of new treatment strategies. © 2013 IUBMB Life, 65(5):409–422, 2013.