Mycosporine-like amino acids (MAAs) strongly absorb UVR and protect cells against harmful UVR. Using spectroscopic and HPLC analysis, two MAAs were detected, i.e. shinorine and porphyra-334, in the pure culture of Microcystis aeruginosa isolated from Lake Taihu and in the phytoplankton samples of Lake Taihu dominated by Microcystis. Synthesis of MAAs could be one of the adaptive strategies to high solar radiation including UVR and one of the bloom-forming mechanisms in Microcystis aeruginosa.