The aim of this study was to investigate the expression of glutamine metabolism-related proteins to determine whether glutamine is metabolized differently according to breast cancer molecular subtype. We generated a tissue microarray of 702 breast cancer patients and performed immunohistochemical staining for glutamine metabolism-related proteins, including glutaminase 1 (GLS1 (GLS)), glutamate dehydrogenase (GDH (H6PD)), and amino acid transporter-2 (ASCT2 (SLC1A5)), which were separately evaluated in tumor and stroma compartments and then analyzed by breast cancer molecular subtypes. Breast cancers were classified as follows: 293 luminal A (41.7%), 166 luminal B (23.6%), 67 HER2 type (9.6%), and 176 TNBC (25.1%). HER2 type showed the highest stromal GLS1 (PZ0. 001), tumoral GDH (PZ0. 001), stromal GDH (P! 0.001), and tumoral ASCT (P! 0.001) expression. We identified differential expression of glutamine metabolism-related proteins according to molecular subtype of breast cancer. The highest glutamine metabolic activity was seen in HER2-type breast cancer.