A novel selenylated low molecular weight apple pectin (Se-LMWAP) was prepared through enzymatic modification combined with selenylation. The physicochemical properties, the structural characterization of Se-LMWAP were evaluated by FT-IR, NMR and SEM. Moreover, the antidiabetic activity and potential mechanism of Se-LMWAP were investigated using high-fat diet (HFD)/streptozotocin (STZ)-induced type 2 diabetic mice. The results revealed that the physicochemical properties of Se-LMWAP were distinctly improved after modifications, and the primary structure was not altered significantly compared to apple pectin and low molecular weight apple pectin. Se-LMWAP had a relative molecular weight of 8.91 × 10 Da (accounted for 61.3 %) and total selenium content of 148.3 ± 2.0 μg/g. It consisted of Rha, Ara, Gal, Glc, Xyl and GalA at a molar ratio of 0.093:0.014:0.132:0.020:0.118:0.622, with the selenium substitution occurred at the C-6 position. Se-LMWAP was able to significantly reduce weight loss, hyperglycemia, oxidative stress and liver, kidney and pancreas damage. Additionally, improved glucose tolerance, relieved lipid metabolism disorders, elevated hepatic glycogen content and ameliorated insulin resistance were observed in the Se-LMWAP group. Overall, Se-LMWAP can be used as a promising dietary selenium supplement to exert -antidiabetic effect through modulating hepatic glucose metabolism and liver insulin-signaling transduction and oxidative stress.