Abstract: Objective: To evaluate the expression of glucose-regulated protein 78 (GRP78) in three breast cancer cell lines (MDA-MB-231, MDA-MB-435S, and MCF-7) and to determine its clinical significance. Methods: Reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot were used to amplify GRP78 mRNA and detect protein expression. Using confocal microscopy, we observed the subcellular localization of GRP78. Results: RT-PCR revealed that the expression of GRP78 mRNA was higher in the MDA-MB-231 breast cancer cells than in MDA-MB-435S and MCF-7 cells. The results of Western blot indicated that GRP78 protein expression showed a pattern similar to that of GRP78 mRNA expression across the three groups with the expression of GRP78 protein in MDA-MB-231 cells as the highest among the three groups. GRP78 protein was mainly expressed in the cytoplasm, membrane and nucleus.Limited expression of GRP78 protein was observed in MCF-7 cells. Conclusion: GRP78 may play a key role in the carcinogenesis and development of breast cancer.