The seaweed Hizikia fusiformis is rich in protein, carbohydrates, vitamins, and minerals. This study investigated the antioxidant and physiological activities of H. fusiformis extracts prepared with 70% ethanol, 80% methanol, or distilled water. The extraction yields of these various solvent extracts were as follows: ethanol extract, 15.26%; methanol extract, 17.95%; and water extract, 45.62%. The methanol extract showed the highest total polyphenol content (24.06 ㎎ GAE/g), but total flavonoid content was similar in all extracts. ABTS (2,2’-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) radical scavenging activity was highest in the ethanol extract (IC<SUB>50</SUB>: 0.90 ㎎/mL), while the methanol extract exhibited the strongest DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity (IC<SUB>50</SUB>: 8.09 ㎎/mL), reducing power (EC<SUB>50</SUB>: 0.40 ㎎/mL), and ferric reducing antioxidant power (0.28 mM). By contrast, tyrosinase and α-glucosidase inhibitory activities were higher in the ethanol extract than in the other extracts. The high BACE1 (β-secretase) inhibitory activity was observed in the ethanol extract (IC<SUB>50</SUB>: 1.03 ㎎/mL). These results indicate that H. fusiformis ethanol extracts may be useful for their antioxidant and functional properties in food and pharmaceutical materials.