The principal objective of this study was to determine the optimal conditions for making muffins with sea-tangle powder, which is known to be a healthy food supplement. The characteristics of the sea-tangle muffins were analyzed in a quality evaluation. Sea-tangle powder was added to the muffins at concentrations of 0%, 5%, 10%, 15%, 20% prior to baking. The height of the muffins to which the sea-tangle powder had been added, after storage at $20^{circ}C$, was shown to decrease with increases in the concentration of sea-tangle powder. The weight of the muffins increased with increasing storage time, but these differences were not profound. The moisture content of the muffins decreased with increased storage time. The change in pH in accordance with storage time differed only slightly. In terms of the color of the sea-tangle powder-supplemented muffins, after storage at $20^{circ}C$, the “L” and “b” values decreased with increasing amounts of added sea-tangle powder. The “a” value increased with increasing amounts of added sea-tangle powder. With regard to the textural properties of the sea-tangle powder-supplemented muffins, after storage at $20^{circ}C$, the hardness and chewiness increased with greater quantities of added sea-tangle powder. Springness, cohesiveness, and adhesiveness differed only slightly as more sea-tangle powder was added. With regard to the sensory characteristics of the muffins, the overall quality of the muffin to which 10% sea-tangle powder was added was evaluated as the best. The color, flavor, and softness were also assessed as the highest. The sweetness of the muffins was assessed as weak.