The objective of this study was to explore the clinical significance of measuring serum free light chains (sFLC) and to compare with serum total light chains (free and binded) in multiple myeloma (MM). sFLC in 20 newly diagnosed MM patients and 20 cases of healthy people as control were measured by immuno-nephelometric assays; the serum light chains and kappa/lambda ratio were measured in all patients, while immunofixation electrophoresis (IFE) tests were carried out at the same time in 18 out of 20 patients. The results showed that the abnormality of serum free light chains and kappa/lambda ratio were found in all of the 20 newly diagnosed MM patients (p < 0.01). The measurement of sFLC showed higher sensitivity than the total serum chains (p < 0.01). It is concluded that the method testing sFLC by immuno-nephelometric assay combined with kappa/lambda ratio is valuable for MM diagnosis, and the measurement of sFLC can be used as one of indicators for MM diagnosis.