The transcription factor nuclear factor kappaB (NF-kB) is a key regulator of inflammation, immune responses and cancer. NF-kB family is considered of five subunits, which are RelA/p65, RelB, c-Rel, p105/p50 and p100/p52. Theoretically, there are 15 possible dimers can be assembled by five NF-kB subunits, 12 of these 15 dimers have been found in vivo. IBs were firstly identified as inhibitors of NF-kB. Further research has revealed that rather than inhibitor, IBs are multi-functional regulators of NF-kB. While the dynamic control of NF-kB dimer activity vis the IB- NF-kB signaling module is well understood, there is little information on how specific dimer repertoires are generated from Rel family polypeptides. Here we identify the roles of Bcl3 in p52 homodimer formation. Our results shown that Bcl3 could competes with RelB and enhances the generation of p52 homodimer.