Abstract:A study is carried out on three freshwater species of Gyrosigma using light and scanning electric microscopy. These three species (Gyrosigma obtusatum, G. kuetzingii and G. sciotoense) all belong to the section Strigiles and all present two types of valve outline in valve view: S-shaped and ?-shaped. Gyrosigma obtusatum has weakly sigmoid valve outline, T-shaped external proximal raphe fissures, straight internal proximal raphe ending, and elliptic central area. Gyrosigma kuetzingii bears distinctly sigmoid valve outline, external proximal raphe fissures which slightly deflect towards different sides, straight internal proximal raphe ending, and elliptic central area. Gyrosigma sciotoense possesses also weakly sigmoid valve outline, strongly hooked external proximal raphe fissures, T-shaped internal proximal raphe fissures, and oblique central area. Gyrosigma obtusatum is found in Gongdong, Gongxi, Hunan, Sichuang and Yunnan; G. kuetzingii is found in both XinJiang and Hunan; and G. sciotoense is only found in Wuling Mountains, and this is its first report from the freshwater in China.