Sperm-associated antigen 5 (SPAG5) is currently considered to serve a role in promoting tumor cell growth and is overexpressed in several types of human cancer. However， to the best of our knowledge， the association of SPAG5 with molecular subtypes of patients with breast cancer (BC) remains to be fully investigated. Reverse transcription-quantitative polymerase chain reaction and immunohistochemistry on tissue microarrays were used in the current study to detect the expression levels of SPAG5 mRNA and protein， respectively， in BC. The association between SPAG5 mRNA and protein levels， and clinical characteristics and prognostic information were investigated. SPAG5 mRNA and protein levels were identified to be higher in BC tissues compared with matched adjacent nontumor tissues. High expression level of SPAG5 protein was associated with tumor size， histological grade， estrogen receptor expression， Ki-67 expression， lymph node status， tumor-node-metastasis (TNM) stage and the triple-negative BC subtype. In addition， high expression level of SPAG5 protein was associated with a poor prognosis in patients with BC. In summary， the current study suggests that SPAG5 is a novel and useful prognostic biomarker in BC.