Emerging evidence greatly implicates that microRNA-450a (miR-450a) plays an essential role in cancer pathobiology. While the pathological role of miR-450a in breast carcinogenesis remains enigmatic. Herein, we showed that miR-450a was lowly expressed in breast cancer cell lines compared with normal, and low miR-450a expression was associated with poor survival in patients with breast cancer. We revealed that miR-450a mimic transfected breast cancer cells (T47D and BT474) exhibited attenuated capacities of proliferation, migration, and invasion in vitro, and miR-450a suppressed T47D cell growth in a xenograft tumor model. Mechanistically, cAMP response element-binding protein 1 (CREB1) was negatively targeted by miR-450a, and CREB1 deletion mimicked the effects of miR-450a mimic treatment. Bioinformatics analysis further revealed that elevated expression of CREB1 correlated with poor prognosis in patients with breast cancer and miR-450a level was negatively correlated with CREB1 level in breast cancer. Additionally, miR-450a inhibited the phosphorylation of phosphatidylinositol 3-kinase/V-akt murine thymoma viral oncogene homolog (PI3K/AKT) and the activities of matrix metalloproteinase-2/9 (MMP-2/9). The following rescue assay indicated that CREB1 was implicated in the anti-tumoral effect of mR-450a in breast carcinoma. All these observations disclosed that miR-450a negatively regulates the growth and metastatic property of breast carcinoma cells.