Dysregulation of lipid metabolism is common in breast cancer. However, the underlying mechanisms remain elusive and the contribution of aberrant lipid metabolism to the malignant phenotypes of breast cancer is poorly understood. Here, we show that the nuclear protein p54(nrb)/Nono is highly expressed in breast cancer tissues as compared with the adjacent normal tissues in human patients. To determine the functions of p54(nrb) in breast cancer, we performed a biochemical screen and identified SREBP-1a, a master activator for genes involved in lipid biosynthesis, as a novel interacting protein of p54(nrb). In human breast cancer tissues, the levels of p54(nrb) and SREBP-1a proteins were positively correlated with each other. Our biochemical analyses showed that the conserved Y267 residue of p54(nrb) was required for its binding to the nuclear form of SREBP-1a. Interestingly, p54(nrb) binding to nuclear SREBP-1a caused an increase of nuclear SREBP-1a protein stability. As a result, p54(nrb) stimulates SREBP-1-meidated transcription of lipogenic genes and lipid production in breast cancer cells. Moreover, both p54(nrb) and SREBP-1a were required for breast cancer cell growth in vitro, and p54(nrb) binding to nuclear SREBP-1a was also critical for breast tumor development in vivo. Together, we conclude that p54(nrb) is a novel regulator of SREBP-1a in the nucleus, and our data suggest that p54(nrb) regulation of SREBP-1a supports the increased cellular demand of lipids for breast cancer growth. Thus, the SREBP pathway may represent a novel target for treating breast cancer.