In the past decade, mechanisms underlying allergic contact dermatitis have been intensively investigated by using contact hypersensitivity (CHS) models in mice. However, the regulatory mechanisms, which could be applicable for the treatment of allergic contact dermatitis, are still largely unknown. To determine the roles of B and T lymphocyte attenuator (BTLA), a CD28 family coinhibitory receptor, in hapten-induced CHS, BTLA-deficient (BTLA -/-) mice and littermate wild-type (WT) mice were subjected to DNFB-induced CHS, severe combined immunodeficient (SCID) mice were injected with CD4 + T cells, and CD8+ T cells from either WT mice or BTLA -/- mice were subjected to CHS. BTLA-/- mice showed enhanced DNFB-induced CHS and proliferation and IFN-γ production of CD8+ T cells as compared with WT mice. SCID mice injected with WT CD4+ T cells and BTLA-/- CD8+ T cells exhibited more severe CHS as compared with those injected with WT CD4+ T cells and WT CD8+ T cells. On the other hand, SCID mice injected with BTLA-/- CD4+ T cells and WT CD8+ T cells exhibited similar CHS to those injected with WT CD4+ T cells and WT CD8+ T cells. Finally, to evaluate the therapeutic potential of an agonistic agent for BTLA on CHS, the effects of an agonistic anti-BTLA antibody (6A6) on CHS were examined. In vivo injection of 6A6 suppressed DNFB-induced CHS and IFN-γ production of CD8+ T cells. Taken together, these results suggest that stimulation of BTLA with agonistic agents has therapeutic potential in CHS.