Abstract: The preliminary double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) for detecting Mg Antigen and the prevalence of Mg infection in STD clinic patients by this method were reported. The results showed that the method had better sensitivity and specificity and was suitable for detection on Mg antigen in the clinical specimens from urogenital tract. The detection results of clinical specimens showed that Mg antigen positive rate in Tianjin and Jiangmen were 12% and 19% respectively. There was Mg infection in the tow areas.