The SERS spectra of serums from the healthy persons and rash patients were measured. In the serum of rash,the band of amide Ⅰ appeared at 1648cm-1,while this peak vanished in healthy serums. The relative intensity of 637cm-1 assigned to the gauche conformation of C—S increased 23% and the band at 725 cm-1 corresponding to anti-conformation decreases 60%. These indicate that the structure of the protein has changed in serums from the rash patients. The relative intensity at 1449cm-1 assigned to the lipids increased nearly one time. The band at 1099cm-1 assigned to the Man—D vanished,indicating that the contents of lipids,glucide and protein increased in rash patients. These results may offer a powerful experiment basis for rash diagnosis and biochemistry mechanism study. The multivariate statistical methods of principal component analysis (PCA) were also used to analyze the SERS of the serums from healthy persons and rash patients,it can be seen that the regional distribution of rash is wider than healthy volunteers,showing that these serums can be discriminated by PCA.