Background: ATG has been employed to deplete T cells in several immune-mediated conditions. However, whether ATG administration affects naive and memory T cell differently is largely unknown. The context and purpose of the study: In this study, we assessed how murine ATG therapy affected T cell subsets in NOD mice, based on their regulatory and naive or memory phenotype, as well as its influence on antigen-specific immune responses. Results: Peripheral blood CD4+ and CD8+ T cells post-ATG therapy declined to their lowest levels at day 3, while CD4+ T cells returned to normal levels more rapidly than CD8+ T cells. ATG therapy failed to eliminate antigen-primed T cells. CD4+ T cell responses post-ATG therapy skewed to T helper type 2 (Th2) and possibly IL-10-producing T regulatory type 1 (Tr1) cells. Intriguingly, Foxp3+ regulatory T cells (Tregs) were less sensitive to ATG depletion and remained at higher levels following in vivo recovery compared to controls. Of note, the frequency of Foxp3+ Tregs with memory T cell phenotype was significantly increased in ATG-treated animals. Conclusion: ATG therapy may modulate antigen-specific immune responses through inducing memory-like regulatory T cells as well as other protective T cells such as Th2 and IL-10-producing Tr1 cells.