The study was undertaken to determine the effect of the aqeuous extract of sea tangle, Laminaria japonicus, on the activites of glucokinase and hexokinase in the pancreas of diabetic mellitus mice which were induced by alloxan. After one week of alloxan injection, the levels of serum glucose and insulin secretion were dramatically increased, however, the insulin secretion was decreased with administration of sea tangle extract. Alloxan injection allowed the serum glucose level to increase and level was decreased by sea tangle extract administration. Furthermore, it was observed the sea tangle extract was effective in recovering the levels of insulin secretion. Enzyme activities of the glucokinase and hexokinase were decreased by alloxan treatment. In contrast, sea tangle extract administration to the mice allowed to increase proportionally. These results suggested that sea tangle extract is highly effective in treatment of diabetic mellitus induced by alloxan.