Tumor cells metabolize more glucose to lactate in aerobic or hypoxic conditions than normal cells. Pyruvate kinase isoenzyme type M2 (PKM2) is crucial for tumor cell aerobic glycolysis. We established a role for let‐7a‐5p/Stat3/hnRNP‐A1/PKM2 signaling in breast cancer cell glucose metabolism. PKM2 depletion via small interfering RNA (siRNA) inhibits cell proliferation and aerobic glycolysis in breast cancer cells. Signal transducer and activator of transcription 3 (Stat3) promotes upregulation of heterogeneous nuclear ribonucleoprotein (hnRNP)‐A1 expression, hnRNP‐A1 binding to pyruvate kinase isoenzyme (PKM) pre messenger RNA, and the subsequent formation of PKM2. This pathway is downregulated by the microRNA let‐7a‐5p, which functionally targets Stat3, whereas hnRNP‐A1 blocks the biogenesis of let‐7a‐5p to counteract its ability to downregulate the Stat3/hnRNP‐A1/PKM2 signaling pathway. The downregulation of Stat3/hnRNP‐A1/PKM2 by let‐7a‐5p is verified using a breast cancer. These results suggest that let‐7a‐5p, Stat3, and hnRNP‐A1 form a feedback loop, thereby regulating PKM2 expression to modulate glucose metabolism of breast cancer cells. These findings elucidate a new pathway mediating aerobic glycolysis in breast cancers and provide an attractive potential target for breast cancer therapeutic intervention.