Objective To investigate the effect of molecular subtype on the margin statusof breast⁃conserving surgery（BCS）and prognosis. Methods We retrospectively reviewed the clinical and histopathologic data of 1 032 consecutive womenat the time of diagnosis with breast cancer deemed suitable for BCS treated with lumpectomy. Univariate and multivariate analyses were used to determine the relationship between the molecular subtype，age， tumor size and positive surgical margins and prognosis. Results 20.3% of the（209/1 032）patients had evidence of cancer intheir cavity margins（CM）. By multivariate analysis，the HER⁃2 BC subtype，EIC，pN stage were sig⁃ nificantly correlated with positive CMs（P < 0.01）. Kaplan ⁃Meier survivalanalysis revealed statistically significant differencesin DFS，LRRFS，and DMFS，among the breast cancer subtypes（P < 0.05）. Conclusion The HER⁃2 positive subtype is the predictive factor that is most associated with positive CMs. The luminal⁃HER⁃2 and HER⁃2 subtypesareindependent prognostic factors for worse outcomes in patients with breast⁃conserving surgery.