Abstract: Glycosylation is a ubiquitous and crucial post-translational protein modification, and tumor tissues have significantly aberrant protein glycosylation alterations as compared to normal tissues. Immune checkpoints are frequently glycosylated in the tumor microenvironment, and their glycosylated forms play a role in protein stabilization and regulation of protein functions. Immunological checkpoint molecules with numerous N-glycosylation sites, such as programmed death-1 (PD-1) and programmed death ligand 1 (PD-L1), contain glycosylation alterations that impede proteasome breakdown, reduce anti-tumor immunity, and increase immune escape of tumor cells. This paper reviews the effects of glycosylation modification on the expression and function of immune checkpoint molecules in the tumor immune microenvironment, and we anticipate that a new glycosylation intervention strategy will improve the efficacy of tumor immune checkpoint blockade therapy.