Abstract: Peridiniopsis Lemmermann is not only an important genus of freshwater thecate dinoflagellates, but also a freshwater group of bloom-forming dinoflagellates. This genus is defined as peridinioids either lacking or having only one anterior intercalary plate. This includes species with plate formulas: 3-5', 0-1a, 6-7 (8)'', 5''', 2''''. So far, there are about 20 species of Peridiniopsis. However, the study on Peridiniopsis from China is relative weakness. Dinoflagellate samples were obtained from diverse habitats in the investigated areas as lakes, rivers, ponds, pools and temporary waters. The fixed cells were stained with 0.1% Fluorescent Brightener 28 and observed for epifluorescence microscopy (EFM), and also observed for differential interference contrast (DIC) and phase contrast (PC) microscopy using a Leica DM5000B microscope and Leica DFC 320 digital camera. According to the study of specimens from China, 8 species and 1 variety had been described. They were Peridiniopsis berolinensis (Lemmermann) Bourrelly, P. borgei Lemmermann, P. cunningtonii Lemmermann, P. elpatiewskyi (Ostenfeld) Bourrelly, P. kevei Grigorszky et Vasas, P. niei G.X. Liu et Z.Y. Hu, P. penardiforme (Lindemann) Bourrelly, P. penardii (Lemmermann) Bourrelly, P. penardii (Lemmermann) Bourrelly var. robusta Q. Zhang, G.X. Liu et Z.Y. Hu. The morphological features, plate pattern, habitat and distribution of each species were given. Among them, 3 species were first reported from China. They were P. berolinensis, P. borgei and P. kevei. The type specimens of P. niei and P. penardii (Lemmermann) Bourrelly var. robusta originated from China. They were published in foreign journals, and therefore were described in Chinese for domestic researchers. The definition of this genus seemed to be an oversimplification. Although the genus had been divided into several new genera in recent years, a major rearrangement at the genus level should be necessary in the future because of relatively high diversity in plate tabulation and polyphyletic taxa.