In this study, the chemical composition and the antioxidant and antidiabetic properties of S. elaeagnifolium flower (SEFl), fruit (SEFr), and leaf (SEFe) extracts were investigated in vitro and in silico. HPLC-DAD analysis was used to determine the chemical components. Colorimetric techniques were used to identify polyphenols and flavonoids. The antioxidant capacity was determined using DPPH and TAC assays. The antidiabetic activity was examined using the enzymes α-amylase and α-glucosidase. Molecular docking methods were used to assess the anti-dipeptidyl peptidase IV (DPP-IV) activity. According to HPLC findings, extracts of S. elaeagnifolium flowers, leaves, and fruits are rich in salicylic acid, sinapic acid, chlorogenic acid, naringin, quercetin, quercetin-3-O-beta-glucoside, kaempferol, and chalcone. The IC₅₀ for flower, leaf, and fruit extracts were 132 ± 5.59 μg/mL, 43.19 ± 1.46 μg/mL, and 132 ± 5.59 μg/mL, respectively. The total antioxidant capacity of SEFr, SEFe, and SEFl were determined to be 900.06 ± 4.01 μg AAE/mg, 792.10 ± 6.72 μg AAE/mg, and 681.10 ± 3.02 μg AAE/mg, respectively. Importantly, SEFe, SEFl, and SEFr displayed significant anti-α-amylase activity, with IC₅₀ values of 79.16 ± 2.35 µg/mL, 99.16 ± 1.17 µg/mL, and 40.31 ± 2.04 µg/mL, respectively. The results also showed that SEFr, SEFe, and SEFl all exhibited potent anti-α-glucosidase activity, whose IC₅₀ values were determined to be 20.53 ± 0.37 µg/mL (SEFr), 20.05 ± 0.12 µg/mL (SEFe), and 41.1 ± 1.55 µg/mL (SEFl). Molecular docking of S. elaeagnifolium phenolic compounds in the active site of DPP-IV revealed a strong inhibitory effect, with a glide score ranging from −2.63 to −8.10 Kcal/mol. Notably—with glide scores of −8.10, −6.23, −5.73, and −5.37 Kcal/mol—rutin, quercetin-3-O-beta-glucoside, chalcone, and naringin were the most active molecules against DPP-IV.