Transglutaminase 2 (TG2) has been reported to play a role in dendritic cell activation and B-cell differentiation after immunization. Its presence and role in T cells, however, has not been explored. In the present study, we determined the expression of TG2 on mouse T cells, and evaluated its role by comparing the behaviours of wild-type and TG2−/− T cells after activation. In our results, naive T cells minimally expressed TG2, expression of which was increased after activation. T-cell proliferation, expression of activation markers such as CD69 and CD25, and secretions of interleukin-2 and interferon-γwere suppressed in the absence of TG2, presumably due, in part, to diminished nuclear factor-κB activation. These effects on T cells seemed to be reflected in thein vivoimmune response, the contact hypersensitivity reaction elicited by 2,4-dinitro-1-fluorobenzene, with lowered peak responses in the TG2−/− mice. When splenic T cells from mice immunized with tumour lysate-loaded wild-type dendritic cells were re-challengedex vivowith the same antigen, the profile of surface markers including CD44, CD62L, and CD127 strongly indicated lesser generation of memory CD8+ T cells in TG2−/− mice. In the TG2−/− CD8+ T cells, moreover, Eomes expression was markedly decreased. These results indicate possible roles of TG2 in CD8+ T-cell activation and CD8+ memory T-cell generation.