Abstract: The detection of serum anti-nDNA antibody using ELISA pretreated with protamin sulfate is reported in this paper Preliminary research on a number of influential factors in the assay were also made. The results suggest that this method is sensitive and reproducible, and the nDNAs stock solution can be used for about 6 month. According to the criteria defined as positive at 1/10 serum dilution and OD≥1.0, 76.7% of the patients with SLE and 90% of the active SLE patients are positive.