The aim of this study was to investigate the preventive effect of Agrocybe chaxingu polysaccharide on streptozocin (STZ)-induced pancreatic ${eta}$-cells destruction. Agrocybe chaxingu polysaccharide markedly reduced nitric oxide (NO) production and iNOS expression levels in RINm5F cells in a dose-dependent manner. In addition, Agrocybe chaxingu polysaccharide significantly inhibited iNOS expression and blood glucose levels in STZ-induced diabetic mice. Moreover, immunohistochemical analysis revealed that it enhanced pancreatic ${eta}$-cells resistance to destruction by STZ. These results suggest that Agrocybe chaxingu polysaccharide may have value as a therapeutic agent against diabetes mellitus.