That paper deals with the studies on the distributiou of fucose in the frond of cul-tivated Laminaria japonica on the methods for isolating fucoidan from the alkali--coagu-lants--the waste residue from the comprehenesive utilization of Laminaria. The content of fucose in Laminaria frond is higher in the marginal portion than inthe middle portion, and longitudinally it increases from 0. 3% in the basal part to morethan 1% in the distal part. (Fig. 1 and Table 1) Two methods of isolating fucidan from the alkali-coagulants were tested, i. e., thecetyl pyrimidium chlorid (CPC) precipitation method and the alcohol arecipitationmethod. (Fig. 2, b) The yields of fucoidan obtained by the two methods are 5.6% and4.4% (to the alkalicoagulants at dry state), and the fucose content are 24.7% and28.7% re,spectively. (Table 4, 5, 6) The content of fucose in alkali--coagalants amounts to 1.4--3.5%. (Table, 3) On acid hydrolysis of the crude fucoidan and subscquent treatment including deioni-zation, evaporation, etc. were applied, the fucose crylals settled out in absolute alcoholafter several days with a trace amount of galactose detected by paper chromatograph andwere further purified by dissolving with methanol--acetone mixture and thus rearystal-lization occurred with only a single spot of fucose shown on paper chromatograpgh.