We investigated the function of circular RNA circEIF3M (hsa_circ_0003119) in triple-negative breast cancer. The expression profiles of circRNAs in 3 specimens of triple-negative breast cancer tissues with adjacent nontumor tissues were analyzed by RNA-sequencing. We verified the oncogenic role of circEIF3M in triple-negative breast cancer through a series of biological function experiments. It was found that circEIF3M was markedly upregulated in triple-negative breast cancer as compared to adjacent nontumor tissue, and that circEIF3M promoted triple-negative breast cancer cell proliferation, migration, and invasion. Mechanistic analysis indicated that circEIF3M may act as a competing endogenous RNA for miR-33a that relieves the inhibitory effect of miR-33a on its target cyclin D1. These findings showed that circEIF3M promotes triple-negative breast cancer progression via the circEIF3M/ miR-33a/ cyclin D1 axis.