The dietary supplement and prebiotic values of β-glucan-rich products have been widely recognized and dietary approaches for modulating autoimmunity have been increasingly explored， we assess the impact of oral administration of high-purity yeast β-glucan (YBG) on gut immune function， microbiota and type 1 diabetes (T1D) using mouse models. Oral administration of this non-digestible complex polysaccharide caused a dectin-1-dependent immune response involving increased expression of interleukin-10 (IL-10)， retinaldehyde dehydrogenase (Raldh) and pro-inflammatory cytokines in the gut mucosa. YBG-exposed intestinal dendritic cells induced/expanded primarily Foxp3 ， IL-10 and IL-17 T cells， ex vivo. Importantly， prolonged oral administration of low-dose YBG at pre-diabetic stage suppressed insulitis and significantly delayed the appearance of T1D in non-obese diabetic (NOD) mice. Further， prolonged treatment with YBG showed increased Foxp3 T-cell frequencies， and a significant change in the gut microbiota， particularly an increase in the abundance of Bacteroidetes and a decrease in the Firmicute members. Oral administration of YBG， together with Raldh-substrate and β-cell antigen， resulted in better protection of NOD mice from T1D. These observations suggest that YBG not only has a prebiotic property， but also an oral tolerogenic-adjuvant-like effect， and these features could be exploited for modulating autoimmunity in T1D.