Purpose: Conditional relative survival (CRS) could provide more relevant information on the current prognosis of cancer survivors than standard 5-year relative survival (RS). This study aimed to estimate the 5-year CRS of Korean breast cancer patients. Patients and Methods: We identified 145,083 breast cancer cases with diagnosis between 2002 and 2013 in the Korea Central Cancer Registry. The CRS was estimated for every year after diagnosis, according to sex, age, histologic types, stage, and year of diagnosis. Results: The 5-year RS at diagnosis was 90.8% and 10-year RS was 85.7%. Five-year CRS was 91.0% and 94.3% at 1-year and 5-year after diagnosis. Women had better 5-year CRS than men after 5 years of survival (94.3% vs. 79.5%), and very young and very old patients had worse 5-year CRS after 5 years of survival than other age groups (92.2% in <40yr, 92.6% in ≥70yr vs. 95.4% in 40-49, 94.3% in 50-59, and 93.7% in 60-69, relatively). In histologic types, CRS of metaplastic carcinoma has improved from 82.0% to 95.2%, compared to CRS of lobular carcinoma (from 93.1% to 92.5%). Hardly any excess mortality (5-year CRS ≥ 95%) was seen since 7 years after diagnosis. There was hardly any excess mortality at 5 years of survival, for the patients with 40-49 years (95.4%), with localized disease (97.8%), and with metaplastic carcinoma (95.2%). Conclusion: This study showed that CRS of breast cancer survivors in Korea has been improved, which varied by sex, age, stage, and histologic types. These CRS analysis could provide a more detailed information for survival to breast cancer survivors and clinicians. Citation Format: Jung S-Y, Jung K-W, Won Y-J, Kwon Y, Ha J, Kim YA, Kong S-Y, Lee ES. Conditional survival of breast cancer patients: Korean nationwide registry [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-08-24.