Aphanothece sacrum, a freshwater cyanobacterium, is an edible cyanobacterial strain. We identified two compounds belonging to the oxylipin family that possess UV-absorbing abilities and accumulate in the dried sample of A. sacrum. The compounds, named saclipin A and saclipin B, exhibited strong UV-absorption properties with the absorption maxima at 316 and 319 nm, respectively, and the molar extinction coefficients of 26,454 and 30,555 M–1 cm–1, respectively. The chemical structures of saclipin