Mechanisms of tolerance break against desmoglein 3 (Dsg3) in patients with pemphigus vulgaris (PV) producing pathogenic anti‐Dsg3 IgG autoantibodies are unclear. In this study, using a novel PV mouse model involving Dsg3 knockout mice, we investigated the mechanisms leading to production of autoantibodies against Dsg3. Adoptive transfer of Dsg3^–/– splenocytes immunized with recombinant mouse Dsg3 to Rag2^–/– recipient mice expressing Dsg3 resulted in the stable production of anti‐Dsg3 IgG and development of PV phenotypes including oral erosions with suprabasilar acantholysis. When purified T and B cells from Dsg3^–/–, Dsg3^+/– or Dsg3^+/+ mice were mixed with various combinations and transferred to Rag2^–/– mice, pathogenic anti‐Dsg3 IgG production was observed only with a combination of Dsg3^–/– T and Dsg3^–/– B cells but not with the other combinations. These results suggest that loss of tolerance against Dsg3 in both B and T cells is important for the development of autoimmune state of PV.