To the best of our knowledge, no previous study has investigated the association of carcinoembryonic antigen (CEA) and cancer antigen 15-3 (CA15-3) with the prognosis for young patients (≤40 years) with breast cancer. In the present study, preoperative CEA and CA15-3 serum levels were evaluated in the prediction of the prognosis for young patients with breast cancer. In total, 699 patients were recruited, for which the CEA and CA15-3 serum levels had been measured prior to surgery via a blood sample. The optimal cut-off high and low values were determined using receiver operating characteristic curve analysis and Youden's index. The value of CEA and CA15-3 in predicting overall survival (OS) and disease-free survival (DFS) were measured using univariate and multivariate Cox's regression analyses. The cut-off values were 3.38 ng/ml and 12.32 U/ml for CEA and CA15-3, respectively. It was identified that CEA, but not CA15-3, was a predictor for the prognosis of the young patients with breast cancer. Multivariate analysis confirmed that CEA, but not CA15-3, was an independent prognostic marker for all young patients with breast cancer. In total, 623 young patients exhibited decreased levels of CEA; in these patients, CA15-3 with a cut-off value of 12.48 U/ml was an independent prognostic factor for OS and DFS. Preoperative serum CEA may thus serve as an independent predictor of poor prognosis for young patients with breast cancer. However, for low-risk patients with decreased CEA levels, serum CA15-3 may supplement the prediction of overall prognosis.