Abstract: The present paper reports on the results of an experimental study on man-cattle-man infection of Sarcocystis hominis, found in Yunnan Province.About ten thousand sporocysts collected from the feces of persons naturally infected with Sarcocystis hominis were fed to a calf, which was dissected 150 days later. Numerous cysts of Sarcocystis hominis were found in the cardiac and skeletal muscles. By light microscopy, the cyst wall of fresh preparation showed numerous thick, finger-like projections, with maximum length of 7.9μm(Fig,1.). By electron microscopy, the cyst had a regularly folded, with primary wall forming palisade-like protrusions. Numerous sharp invaginations found infthe protrusions were sawtooth-shaped, covering the whole surface of the protrusions (Fig. 3). No fine fibrils were observed within the zone of ground substance beneath the primary cyst wall.Two rhesus monkeys were fed with beef infected with Sarcocystis hominis and sporocysts and oocysts were found in their feces 29 and 31 days later, the patent period of sporocyst excretion bieng 5 and 7 days, respectively.The senior author had taken voluntarily 60g beef of the experimentally infected calf, and presented clinical symptoms such as anaemia, abdominal pain, diarrhoea, fatigus and dizziness on ds post infection with sporocysts and oocysts found in the feces on d,. The patent period of sporocyst excretion was more than 42 days. The mean size of 50 sporocysts was 11.90±0.04 ×15.88± 0.03μm and that of 50 oocysts, 15.56 ± 0.05 × 19.76 ±0.04μm(Fig.4). On d50 he took acetylspiramycine tablets, the initial dose being 0.4g, followed by 0.2g qid. for 15 days. 10 days after acetylspiramycine administration, the symptoms disappeared and so did the sporocysts on fecal examination.