CARMA3 was recently reported to be overexpressed in several cancers and associated with malignant behavior of cancer cells. However, the expression pattern and biological roles of CARMA3 in breast cancer have not been reported. In the present study, we found that CARMA3 was overexpressed in 41.9 % of breast cancer specimens. Significant association was observed between CARMA3 overexpression and TNM stage (p = 0.0223), tumor size (p = 0.0227), and ErbB-2 status (p = 0.0049). Furthermore, knockdown of CARMA3 expression in MDA-MB-435 cells with high endogenous expression decreased cell proliferation and sensitized cell to paclitaxel-induced apoptosis, while overexpression of CARMA3 in MDA-MB-231 cell line promoted cell proliferation and inhibited apoptosis. Further analysis showed that CARMA3 depletion downregulated, and its overexpression upregulated cyclin D1, Bcl-2, and p-IκB levels. In conclusion, our study demonstrated that CARMA3 is overexpressed in breast cancers. CARMA3 facilitates proliferation and inhibits apoptosis through nuclear factor-kappaB signaling.