Abstract: Objective：To establish the reference ranges of serum free light chain ratio (sFLC-R) in Shanghai, and to study the preliminary clinical significance of sFLC-R for plasma cell neoplasm（PCN）diagnosis. Methods：Sixtyfive healthy individuals undergoing ordinary health examinations in Zhongshan Hospital, Fudan University were recruited as the healthy group; 29 patients with kidney disease as the kidney disease group; 27 patients with PCN as the PCN group. All participants enrolled received the serumfree kappa and lambda light chain detection, and sFLC-R was calculated for further analysis. Results：The reference range of serum free light chain ratio was 0.541.15 （97.5% conference interval）. The concentrations of κ and λ FLC in kidney disease group were higher than those in healthy group (P<0.05). The abnormalities ratios of sFLC had a slight difference from that of the disease group, but the difference of the sFLC-R abnormalities ratios was quite apparent. The majority sFLC-Rs in PCN group were outside the reference range, especially the increase of λ FLC. Conclusions：The concentration of serumfree light chain could reflect the dynamic process of plasma cell production and renal excretion, and sFLC could increase in either plasma cell proliferation or decreased glomerular filtration situations. However, sFLCR only showed significant changes under the situations in which expressions of either immunoglobulin or light chain were restricted, but remained normal when glomerular filtration decreased. Therefore, the detection of sFLC-R could be a promising tool for early diagnosis and differential diagnosis of plasma cell diseases.