Abstract: Seven batches of Anopheles dims were used to take blood meal successively from 4 P. vivax-infected patients living in Guizhou Province after "informed consent". Morphological studies with scanning electron microscope on various stages of sporogony on days 9, 11 and 12 post-infection were carried out. The surface features of oocysts were similar to those of other species of the genus Plasmodium. The inner surface of oocyst wall appeared rough and bore many spinal processes (Fig. 5). From the early stage of sporoblast, budded the short cone-shaped sporozoites buds which gradually developed into sporozoites (Figs. 6~9). The sporozoite appeared elongated, curved and invested with smooth plasma-lemma. The microspore was located about 1/3 of the body from the anterior end which was somewhat truncated obliquely (Fig. 10).