Background:　Type　C　behavior　is　a　cancer-prone　behavior　that　can　affect　the　occurrence　and　development　of　cancer.　This　study　aimed　to　investigate　the　prevalence　of　type　C　behavior　in　patients　with　breast　cancer　during　postoperative　chemotherapy　and　determine　its　associated　factors.　Methods:　This　study　enrolled　161　patients　with　breast　cancer　who　received　postoperative　chemotherapy.　Type　C　personality　behavior　pattern　questionnaire　was　used　to　assess　type　C　behavior　patterns.　The　following　instruments　were　employed:　medical　coping　modes　questionnaire,　social　support　scale,　social　relational　quality　scale,　Herth　hope　index.　logistic　regression　was　used　to　identify　the　factors　affecting　type　C　behavior.　Results:　The　incidence　of　type　C　behavior　was　28%.　Participants　aged　45-59　years　(OR　=　3.62,　95%　CI　=　1.04-12.56,　P　=　0.043),　and　who　adopted　a　resignation　coping　style　(OR　=　1.25,　95%　CI　=　1.03-1.50,　P　=　0.021),　were　more　likely　to　develop　type　C　behavior.　Type　C　behavior　was　less　common　in　patients　with　employment　(OR　=　0.38,　95%　CI　=　0.15-0.97,　P　=　0.043),　with　a　high　level　of　social　support　(OR　=　0.89,　95%　CI　=　0.80-0.98,　P　=　0.023),　and　more　hope　(OR　=　0.83,　95%　CI　=　0.71-0.98,　P　=　0.079).　Conclusion:　In　this　study,　28%　patients　with　breast　cancer　during　postoperative　chemotherapy　exhibited　type　C　behavior.　Associated　factors　with　type　C　behavior　were　identified,　which　could　guide　health　care　professionals　to　reduce　the　prevalence　of　type　C　behavior　through　guiding　patients　to　adopt　positive　coping　styles　and　improving　their　level　of　social　support　and　hope,　especially　in　those　aged　45　to　59　years　or　in　those　without　employment.