Abstract: Nostoc commune which belongs to blue-green algae has been observed with microscope, scanning and transmission electron microscopes. The following special structures are found: 1. The structure in thallus is spongiform with an uneven surface. 2. The filaments made up of torulose cells are tortuous with different length, some are piled up, some are branchy, and the others arrange in a circle. 3. The cell wall of torulose cell is five-layered. The outermost layer is ripply and inlays with neighbour cells. 4. Torulose cells are typical prokaryote. The thylakoids disperse in the peripheral plasma. The nucleoplasm exists in the center of the cell. There are structured granules, polyhedral and polyphosphate bodies interspersing in cytoplasm. Ribosomes and phycobilins are found on the surface of thylakoid. 5. The heterocyst is surrounded by a thicking sheath. This is an additional envelope outside the cell wall and can be called “cell envelope”. In the cell envelope exist a transparent layer and a dense electron layer with hemispherical nodule in which there is an channel interlinking up with neighbour cell. 6. The reproductive manner of N. commune is of horizontal split, and the direction of split is different.

Key words: Nostoc commune, Ultrastructure, Torulose cell, Gyanophyta