The sporulation of the pethogen and the distribution of the pathgen hyphae in the diseased tissue and the damage caused by bsmboo culm rust (Stereostratum corticioides) were investigated by using scanning electron microscopes. The main results are as follows: 1. The initial urediospore is a saccate swell of the top of sporogenous cell; there are no warts on the surface; with the development of urediospore, there appear many little warts on its surface and finally the warts become little spiny protuberance. The stalks of the early layer teliospores in the telium are short and thick while the teliospores formed later are long and thin. The uredinia and telia are formed under the cuticle and under one or two layers of epidermal cells, then they break through the epidermal tissue and expose in the air finally. 2. The hyphae can extend in the intercellular space and form infection filamentS which can enter the parenchyma and sieve cells through the holes of the cell wall and then develop into haustoria. 3. The bamboo culm rust only results in the necrosis of the epidermal tissue, but does not destroy the diseased bamboo. The wounds resulted from the formation of the uredinia and telia of the rust provide the locations for later patbogen to infect and grow, and the parasitization and growth of the later pathogen lead to the death of the diseased bamboo.