interleukin 35 (iL-35), a cytokine secreted by regulatory T (Treg) cells from the differentiation of conventional CD4 + T cells, is a member of the iL-12 family. The iL-12 family of cytokines exhibits an anti-inflammatory property. iL-35 has recently been shown to influence the immune modulation in various diseases, including inflammatory bowel disease, Graves' disease, rheumatoid arthritis, colitis, psoriasis, and type 1 diabetes (T1D). T1D is an immune-related disease caused by destruction of pancreatic β cells, characterized by an absolute lack of insulin. Recently, studies have suggested that protective effects of iL-35 work by improving blood glucose levels and preventing an attack of inflammatory factors on the islets. The protective mechanism may be closely related to the anti-inflammatory properties of iL-35, which include regulating macrophage phenotype, suppressing T cell proliferation, decreasing the differentiation of Th17 cells, increasing the Treg cell population, and inducing iL-35-producing regulatory T cells (iTr35). here, we review the protective effects and mechanisms of action of iL-35 in T1D.