Two new 2-amino-2-butenoic acid (Dhb)-containing microcystins (Dhb-microcystins), [D-Asp 3, (E)-Dhb7]microcystin-LR (1) and -HtyR (2), were isolated from Oscillatoria agardhii. The structures were elucidated by the extensive NMR analyses and confirmed by mass spectral and amino acid analyses. The absolute configuration was determined by chemical degradation and chiral GC analyses. The configuration of the Dhb unit of 1 and 2 was determined as E by ROESY experiments.