Breast cancer is the most common cancer and the leading cause of cancer death in women worldwide.1 Tumor-infiltrating myeloid cells (TIMs), key components of tumor microenvironment, are considered to be potential therapeutic targets for cancer recently,2,3 however, their heterogeneity remains insufficiently characterized in different breast cancer subtypes. A more detailed TIM transcriptional atlas across breast cancer subtypes at the single-cell level is required to better understand the underlying mechanisms influencing the prognosis of breast cancer patients. Here, we painted the landscapes of TIMs and investigated the diversity of TIM subsets across breast cancer subtypes. Particularly, we identified a novel subset, CXCL10+ conventional dendritic cells (cDCs), which are abundant in triple-negative breast cancer (TNBC) and have the ability to recruit tumor-associated macrophages (TAMs). We further discovered the developmental origins of CXCL10+ cDCs. Moreover, we identified novel subsets of macrophages and mast cells and systematically analyzed their characteristics associated with clinical outcomes in different breast cancer subtypes. Our findings provide valuable information for the identification of potential targets and biomarkers to better direct breast cancer immunotherapies.