Ypaoamide, a new herbivore antifeedent metabolite, was isolated from the extract of a mixed cyanobacteria assemblage which was composed ofSchizothrix calcicola and Lyngbya majuscula. The structure was determined spectroscopically by interpretation of 2D-NMR experiments, including HMBC and NOESY, and by comparison with model compounds. Isolated cells of the L. majuscula produced ypaoamide in laboratory culture.