Abstract: Objective　To investigate the clinical application significance of free light chain determination in children with viral encephalitis. Methods　Albumin（Alb），immunoglobulin G（IgG）and free light chain were determined in cerebrospinal fluids（CSF） and sera of 24 viral encephalitis children and 12 children without viral encephalitis by BN-II specific protein analyzer. The oligoclonal IgG bands were detected by immunofixation electrophoresis.The Alb CSF/serum quotient（QAlb），IgG CSF/serum quotient（QIgG），kappa CSF/serum quotient（Qκ）and lamda CSF/serum quotient（Qλ）were calculated and analyzed comparatively. Results　The oligoclonal IgG bands were all negative in all children. QAlb，QIgG，Qκ and Qλ in children with viral encephalitis were significantly higher than those in children without viral encephalitis（P<0.01）.QIgG，Qκ and Qλwere significantly higher in blood-brain barrier damage group than in normal group（P<0.01）.In blood-brain barrier damage group，the areas under the receiver operating characteristic curve were 0.884±0.056 for Qκ and 0.878±0.056 for Qλ. Conclusions　Free light chain has application significance for the clinical diagnosis of viral encephalitis in children，and Qκ and Qλ are good indices for the detection of blood-brain barrier damage.

Key words: Free light chain, Albumin, Immunoglobulin G, Viral encephalitis