Multiple myeloma (MM) is a malignant disorder characterized by the proliferation of a single clone of plasma cells that can produce excessive amounts of serum free light chain (sFLC). sFLC plays an important role in MM diagnosis and disease monitoring. The quantitative immuno-nephelometric assay is sensitive and specific means for sFLC testing. The aim of this study was to investigate the levels of sFLC in multiple myeloma and the relationship between sFLC and serum total light chain (sTLC). sFLC in 45 newly diagnosed patients were detected by immuno-nephelometric assay, and then the ratio of free kappa to free lambda for every sample was calculated. Meanwhile, sTLC was also determined in these patients. The results showed that the difference of sFLC levels between MM patients and the normal controls was significant (tΚ = 8.86, P < 0.001; tλ = 15.48, P < 0.001;tΚ/λ = 5.54,P < 0.005). No correlation between sFLC and sTLC was found in MM patients. It is concluded that the level of sFLC in MM patients is significantly higher than that in normal controls. sFLC and its ratio may be served as a indicator for diagnosis of MM. sTLC can not replace the role of sFLC.