Cell division cycle-associated 5 (CDCA5) plays a critical role in the progression of various human cancers by regulating cell cycle-related proteins; however, the function of CDCA5 in breast cancer (BC) is poorly understood. The aim of the present study was to investigate the expression level of CDCA5 in BC and its effect on BC progression. CDCA5 was found to be highly expressed in patients with BC, as well as in BC cell lines. It was also found that a high CDCA5 expression in BC was significantly associated with a shorter survival rate. In addition, the expression level of CDCA5 was significantly increased in stem cells derived from suspension-cultured BC cells, as compared to adherent-cultured cells. CDCA5 knockdown in MCF7 and SKBR3 cells significantly reduced cell proliferation, migration and clone formation. At the same time, the stemness capacity of BC cells, determined by analyzing cancer stem cell marker expression and mammosphere formation, was also markedly diminished following the knockdown of CDCA5. In addition, in vivo experiments demonstrated that CDCA5 knockdown in MCF7 cells markedly reduced tumor growth. On the whole, the present study demonstrates that CDCA5 may be used as a prognostic biomarker and therapeutic target for BC.