Six compounds, kaempferol-3-O-β-d-(6?2?2-O-coumaryl) glycoside, 1-feruloyl-β-d-glucopyranoside, isorhamnetin-3-O-glucoside, quercetin 3-O-β-d-glucopyranoside, quercetin 3-O-β-d-glucopyranosyl-7-O-α±-l-rhamnopyranoside, and isorhamnetin-3-O-rutinoside, were isolated from sea buckthorn leaf extracts. The butanol fraction (EC50 = 1.81 μg/mL) along with quercetin 3-O-β-d-glucopyranoside (EC50 = 1.86 μg/mL) had a higher DPPH radical-scavenging activity and showed stronger reducing power (OD700 = 1.83 and 1.78, respectively). The butanol fraction (477 mg GAE/g) contained the highest amount of phenolic compounds and also the most powerful α±-glucosidase inhibitory effect (86%) at 5 μg/mL.