We have identified a novel CARD-containing protein from EST database, BinCARD (Bcl10-interacting protein with CARD). BinCARD was ubiquitously expressed. Co-immunoprecipitation, In vitro binding, mammalian two-hybrid, and immunostaining assays revealed that BinCARD interacted with Bcl10 through CARD. BinCARD potently suppressed NF-κB activation induced by Bcl10 and decreased the amounts of phosphorylated Bcl10. Mutations at the residue Leu17 or Leu65, which is highly conserved in CARD, abolished the inhibitory effects of BinCARD on both Bcl10-induced activation of NF-κB and phosphorylation of Bcl10. Further, expression of BinCARD inhibited Bcl10 phosphorylation induced by T cell activation signal. These results suggest that BinCARD interacts with Bcl10 to inhibit Bcl10-mediated activation of NF-κB and to suppress Bcl10 phosphorylation.