Two new thiazole-containing cyclic hexapeptides, microcyclamides MZ602 and MZ568, were isolated from the hydrophilic extract of the cyanobacterium Microcystis sp. The structures of the pure natural products were elucidated using spectroscopic methods including UV, 1D and 2D NMR, and MS techniques. The absolute configuration of the chiral centres of the modified cyclic peptides was determined using Marfey's method for HPLC. The microcyclamides have been evaluated for their cytotoxicity against leukemia cell lines and inhibition of serine proteases.