Long non‐coding RNA (lncRNA) is involved in the regulation of tumorigenesis and metastasis. In this study, we focused on the clinical relevance, biological effects, and molecular mechanisms of the lncRNA differentiation antagonizing non‐protein coding RNA (DANCR) in breast cancer. We compared the expression of DANCR between breast cancer and normal tissues, and between breast cancer cell lines and normal breast epithelial cells using quantitative real‐time PCR (qRT‐PCR) analysis. By knocking down and overexpressing DANCR, we assessed its significance in regulating viability (MTT assay), migration/invasion (Transwell assay), epithelial‐mesenchymal transition (western blot), stemness (mammosphere formation assay and western blot), and production of inflammatory cytokines (qRT‐PCR and ELISA) of breast cancer cells in vitro, as well as xenograft growth in vivo. Furthermore, using ChIP and RNA immunoprecipitation, we examined the reciprocal regulation between DANCR and suppressor of cytokine signaling 3 (SOCS3) in breast cancer. DANCR was significantly up‐regulated in tissue samples from patients with breast cancer, as well as in breast cancer cell lines, as compared with normal tissues and breast epithelial cells, respectively. The highest DANCR expression levels were associated with advanced tumor grades or lymph node metastasis. DANCR was necessary and sufficient to control multiple malignant phenotypes of breast cancer cells in vitro and xenograft growth in vivo. Mechanistically, DANCR promoted the binding of enhancer of zeste homolog 2 (EZH2) to the promoter of SOCS3, thereby epigenetically inhibiting SOCS3 expression. Functionally, SOCS3 up‐regulation or EZH2 inhibition could rescue multiple malignant phenotypes induced by DANCR. Our data indicate that DANCR is a pleiotropic oncogenic lncRNA in breast cancer. Boosting SOCS3 expression may reverse the oncogenic activities of DANCR and thus provide a therapeutic strategy for breast cancer treatment. Differentiation antagonizing non‐protein coding RNA (DANCR) binds to enhancer of zeste homolog 2 (EZH2), recruiting EZH2‐ and EZH2‐generated H3K27me3 to the suppressor of cytokine signaling 3 (SOCS3) promoter, thus inhibiting the transcription of SOCS3. DANCR induced down‐regulation of SOCS3‐induced inflammatory response and multiple malignant phenotypes in breast cancer cell.