Reactivation of tumor suppressor genes (TSGs) involved in carcinogenesis by nontoxic bioactive food component represents a promising strategy for cancer chemoprevention. Recently, curcumin has been demonstrated to inhibit a bacterial DNA methyltransferase (M. Sss I) activity, induce global DNA hypomethylation in leukemia cells, and reactivate several hypermethylation silenced genes in lung and prostate cancer cells. Herein, we demonstrated that curcumin can enhance the mRNA and protein levels of ras-association domain family protein 1A (RASSF1A), 1 hypermethylation-silenced TSG, and decrease its promoter methylation in breast cancer cells. Mechanistic study demonstrated that curcumin can decrease DNA methylation activity of nuclear extract and downregulate the mRNA and protein levels of DNMT1 in MCF-7 cells, which may be associated with curcumin-induced disruption of NF-κB/Sp1 complex bound to the promoter region of DNMT1. Altogether, this study reveals a novel molecular mechanism of curcumin as a chemo-preventive agent for breast cancer through hypomethylation reactivation of RASSF1A.