HIV/SIV infection leads to eventual diminished proliferation and loss of functions of CD8+ T cells. Understanding the mechanisms involved in CD8+ T-cell dysfunction and how to reinvigorate it is critical in the strategy to cure HIV. It is known that N-glycosylation modulates T-cell functions in cancer and viral infections by increasing surface retention of exhaustion markers and by preventing antigen recognition at the immune synapse. Galectin-3 (Gal-3), a predominant lectin with a high affinity for glycoprotein, forms a lattice after binding with N-glycan, restricts the clustering of T cell receptors and co-receptors in the immune synapse, and impairs T-cell functions. Herein, we speculate that N-glycosylation modulated by Gal-3 and other involved pathways may negatively impact CD8 + T-cell function in HIV/SIV infection. In this study, eight Chinese rhesus macaques (cRM) were infected with SIVmac239M and treated with antiretroviral therapy daily for over 6 months. CD8+ T cells were isolated from PBMCs at pre-infection and SIV+ on ART time points. Expression of Gal-3 was evaluated by quantitative real-time PCR. N-glycan branching on the CD8+ T cells was analyzed by flow cytometry. Swainsonine, which blocks N-glycosylation by inhibiting a-mannosidase, was used to treat dysfunctional CD8+ T cells purified from PBMCs of ART-suppressed SIV-infected cRM ex vivo. CD8+ T-cell proliferation and cytokine production after swainsonine treatment were evaluated by flow cytometry. We found that, compared to pre-infection, increased Gal-3 in PBMCs and N-glycan branching on CD8+ T cells were observed in ART-suppressed cRM. N-glycosylation inhibited the proliferation of CD8+ T cells. The intervention on N-glycosylation by swainsonine successfully restored the proliferation and increased the cytokine production of CD8+ T cells isolated from ART-suppressed SIV-infected cRM. In conclusion, N-glycosylation contributes to CD8+ T-cell dysfunction during HIV/SIV infection. Therapeutic strategies targeting N-glycosylation may therefore restore this critical antiviral response and enhance viral control.