Abstract: Objective To investigate the infection of Cryptosporidium and other pathogenic germs among HIV/AIDS patients with chronic diarrhea.Methods Stool samples were collected from confirmed HIV/AIDS patients with chronic diarrhea and living in Beijing.The samples were concentrated by formalin-ethyl acetate sedimentation technique and stained by modified acid-fast stain for the identification of oocysts by microscopy.And nest-PCR was adopted.CD4⁺count was detected by flowcytometry.Results The infection rate of Cryptosporidium in the patients was 5.97%(4/67).The bacterial culture detected 60 cases of fungus infection and one case was positive for Clostridium difficile toxin.Conclusion AIDS patients infected by Cryptesporidium are not rare in Beijing,and the infectious rate is not associated with patient's gender but associated with patient's living environment,especailly for the patients living in the countrysides and with lower level of CD4 cells and the patiens in the middle-late period of the disease.