The development of protein utilization with inedible algae (Ulva pertusa Kjellman, Sargassum aumyendo Kjellman) have been investigated. These include a) composition of algae, b) condition fo extractability of crude protein with water and tris buffer, c) precipitation of crude protein with various precipitate agent, d) digestibility of algae diet which was mixed with wheat bran, e) pepsin digestibility of crude protein, and f) the amino acid composition of the algae protein. The results are obtained as follows; (1) Two species of algae examined were good source of protein because they contained 17% to 19% of crude protein; (2) Ulva pertusa Kjellman could be used for an animal diet, and its proper mixing ratio with wheat bran was 25% of algae to 75% of wheat bran, of which the condition reveals the best digestibility; (3) Water was better extractant for protein of the algae than tris buffer, precipitation of protein in boiling water bath was the most economical method of preparation of the protein from algae unless the protein activity was required; (4) For the precipitates from algae between pH $1{sim}12$, its yield was increased in proportion to alkaline concentration; (5) Extractability of protein from algae were not affected by either ascorbic acid or sucrose in tris buffer solution; (6) Aspartic and glutamic acids were the amino acids most abundant in the algae proteins and essential amino acids, especially of leucine, isoleucine, valine, threonine, lysine and tryptophan, were also relatively high in its contents.