The E2 polyubiquitin-conjugating enzyme Ubc13 is a mediator of innate immune reactions. Ubc13 mediates the conjugation of K63-linked polyubiquitin chains onto TRAF6 and IKKgamma during NF-kappaB activation. In contrast to K48-linked polyubiquitin chains, K63-linked polyubiquitin chains function in non-proteasomal biological processes. Although Ubc13 has been shown to be critical for TLR and IL-1 receptor signaling, the function of Ubc13 in the epidermis has not been studied. We generated keratinocyte-specific Ubc13-deficient mice (Ubc13(flox/flox)K5-Cre). At birth, the skin of the Ubc13(flox/flox)K5-Cre mice was abnormally shiny and smooth; in addition, the mice did not grow and died by postnatal day P2. Histological analysis showed atrophy of the epidermis with keratinocyte apoptosis. Immunohistochemical analyses revealed reduced proliferation, abnormal differentiation, and apoptosis of keratinocytes in the Ubc13(flox/flox)K5-Cre mouse epidermis. In culture, Ubc13(flox/flox)K5-Cre keratinocyte growth was impaired and spontaneous cell death occurred. Moreover, the deletion of Ubc13 from cultured Ubc13(flox/flox)keratinocytes by means of an adenoviral vector carrying Cre recombinase also resulted in spontaneous cell death. Therefore, Ubc13 is essential for keratinocyte growth, differentiation, and survival. Analyses of intracellular signaling revealed that the IL-1 and TNF-induced activation of JNK, p38, and NF-kappaB pathways was impaired in Ubc13(flox/flox)K5-Cre keratinocytes. In conclusion, Ubc13 appears to be essential for epidermal integrity in mice.