About fifty common species of Microcystis have been reported worldwide by far, but only twelve species were recently reported in China. Based on field material collected from Lake Taihu, the Microcystis panniformis belonging to Microcystis (Cyanophyta) was reported for the first time in China in this paper. The morphological characteristics of M. panniformis were described in detail. Comparisons among Microcystis and its related genera Pannus were also conducted.