Objective:To construct breast cancer organoid culture system and conduct histological characterization and preliminary radiobiological characteristics study.Methods:Different molecular types of breast cancer cell lines and patient-derived tumor cells were cultured in vitro to form breast cancer organoids and characterize their tissue structure. In addition, Ki-67, ER, PR and Her2 markers were evaluated by immunohistochemical staining. Breast cancer organoids were irradiated with 4 Gy and 8 Gy. The numbe and diameter changes of breast cancer organoids at 0, 24, 48 and 96 h after irradiation were observed to evaluate the irradiation-induced damage to the organoids. Results:Breast cancer cell lines and patient-derived tissues formed organoid structures at 6 d. HE staining showed the microstructures, and the expression profile of markers was spatially heterogeneous. The expression patterns of markers were similar between patient-derived organoids and original tumor tissues. Irradiation of MCF-7 breast cancer organoids led to growth arrested, and some of the formed organoids collapsed and the proliferating trend gradually recovered from 48 h to 96 h. MDA-MB-231 breast tumor organoids showed radioresistance, growth arrested, but the structures remained intact, the recovery trend was still not observed at 96 h. The tissue-derived organoids from triple-negative patients also showed radiation tolerance. After irradiation, the organoids continued to grow without significant structural changes, whereas the growth trend was significantly smaller than that in the non-irradiated group.Conclusions:Breast cancer organoids formed by in vitro culture of breast cancer cells from different sources and different molecular types have microstructure and heterogeneity, which can reflect the expression of source tissue markers and show different radioresistance. Organoids derived from triple-negative breast cancer are more resistant to irradiation.