PURPOSE: To assess the relationship between the kinetics of the serum CA15-3 level and the five-year disease-free survival rate of breast cancer patients. METHODS: The subjects of this study, 297 women who were diagnosed with breast cancer, were the subset of patients operated on at Kosin University Gospel Hospital from January 2008 to December 2010. We evaluated the change of serum CA15-3 levels during outpatient follow-up period. The changing patterns of serum CA15-3 level were divided into 5 categories; surge without decline, surge with incidental decline, decline without surge, decline with incidental surge, and no change. Clinicopathologic factors were evaluated for each group. RESULTS: The number of patients in surge without decline, surge with incidental decline, decline without surge, decline with incidental surge, and no changes groups were 30 (10.1%), 85 (28.6%), 80 (26.9%), 73 (24.6%), and 29 (9.7%), respectively. The clinicopathologic characteristics were not significantly different among these groups. The log rank test found that 5-year disease-free survival rate according to the kinetics of serum CA15-3 levels were significant (P = 0.004) particularly for the surge without decline group. CONCLUSION: According to the findings of this study, the surge without incidental decline pattern of serum CA15-3 levels during the follow-up period is associated with poor prognosis. Significant association was found among changing patterns of serum CA15-3 levels and breast cancer recurrence rate.