A case of life-threatening chronic diarrhea, caused by Cryptosporidium spp., was reported. The patient was a seven month old boy from an orphanage suffering from voluminous watery diarrhea, fever and vomiting three days before admission. He presented with severe dehydration and severe hypokalemia. Numerous cryptosporidial oocysts were detected in the stools without other enteropathogens. Although co-trimoxazole and gentamicin were administered in the first week of illness, the diarrheal symptom was still persistent. At the end of the third week, spontaneous remission was observed. The overall diarrheal period lasted twenty-five days. In this case, cryptosporidiosis manifested as severe chronic diarrhea in the immunocompetent and supportive management was very important because an effective drug is not available at present.