Genistein possesses a wide variety of biological activities, and it is best known for its ability to inhibit cancer progression. Its cancer-preventive effect has been attributed to various mechanisms, including the induction of cell cycle arrest and apoptosis as well as the antioxidant functions. Nuclear factor kappa-B (NF-κB) is a signaling pathway that controls transcriptional activation of genes important for the tight regulation of many cellular processes and is aberrantly expressed in many types of cancer. Inhibitors of NF-κB pathway have shown potential anti-tumor activities. However, it is not fully elucidated in colon cancer. In the present study, we demonstrated that genistein could induce apoptosis in human colon cancer LoVo and HT-29 cells through inhibiting NF-κB pathway, as well as downregulation of Bcl-2 and upregulation of Bax, thus providing basis for clinical application of genistein in colon cancer cases.