Objective To explore the microRNAs regulation of CXC chemokine ligand 13 (CXCL13) in patients with myasthenia gravis combined with thymic hyperplasia (MGH).Methods Thirteen MGH tissues and 13 normal thymus tissues,collected in our hospital from March 2012 to August 2013,were used in our study.Total RNAs from these tissues were extracted by trizol and hybridized with the microarray.The miRNAs targeting CXCL13 gene-3'untranslated region were predicted by using bioinformatics.Real-time fluorogenic quantitative PCR (QRT-PCR) was employed to detect the expressions ofCXCL13 mRNAs and microRNAs in thymus tissues.Luciferase assay was used to analyze the miRNAs modulated CXCL13 expression.Results The miRNA microarray chip analysis identified 33 miRNAs differentially expressed in MGH tissues as compared with those in the control group,miR-548k was one of most obvious down-regulated miRNAs (1.98 fold).Bioinformatical analysis indicated that miR-548k can target CXCL13 3' UTR.QRT-PCR showed that the expression of CXCL13 mRNA was up-regulated and miR-548k was down-regulated in thymus hyperplasia tissues of MGH group as compared with those in the control group(4.93±l.95 vs.1.04±0.20; 0.55±0.20 vs.1.33±0.36,P＜0.05); and they showed a negative correlation (r=-0.93,P=0).003).As compared with that in the control group (1.000±0.050),the luciferase activity of pmiR-RB-REPORTTM-CXCL13-3'UTR treated with miR-548k mimics (0.385±0.016) decreased 61.5％,with significant difference (P＜0.05).Conclusion MiR-548k inhibits CXCL13 expression by post-transcriptional gene silencing to promote MG development and progression.