RAF6, TNFR-associated factor 6, is an essential adaptor downstream from the TNF receptor and TLR superfamily members. This molecule is critical for dendritic cell maturation and T cell homeostasis. Here, we show that TRAF6 is important in high affinity IgE receptor, FcepsilonRI-mediated mast cell activation. In contrast to dendritic cells and T cells, TRAF6-deficient mast cells matured normally and showed normal IgE-dependent degranulation. Importantly, TRAF6 deficient mast cells showed impaired production of cytokine IL-6, CCL-9, IL-13 and TNF following FcepsilonRI aggregation. Chromotin immunoprecipitation assay showed decreased NF-kappaB p65 binding to CCL-9 and TNF promoters in TRAF6-deficient mast cells. Antigen and IgE-induced IkappaB phosphorylation and NF-kappaB p65 translocation to the nucleus were diminished in TRAF6-deficient mast cells. NF-kappaB luciferase activity in response to antigen and IgE stimulation was severely impaired in TRAF6-deficient mast cells. In addition, antigen and IgE-induced phosphorylation of MAP kinase p38 and JNK, but not ERK1/2 was significantly reduced in TRAF6-deficient mast cells. These results identified TRAF6 as an important signal transducer in FcepsilonRI-mediated signalling in mast cells. Our findings implicate TRAF6 as a new adaptor/regulator molecule for allergen-mediated inflammation in allergy.