Background. Treponema pallidum subspecies pallidum (T. pallidum) infection induces significant immune responses, resulting in tissue damage. Gene expression plays an essential role in regulating the progression of syphilis infection. However, little is known about the regulatory role of microRNAs (miRNAs) in the immune response to T. pallidum infection. Here, we analyze the differential expression of miRNAs in peripheral blood mononuclear cells (PBMCs) between untreated secondary syphilis patients and healthy controls and study the correlation between miRNA expression and clinical features with bioinformatics. Methods. The expression profile of miRNAs was measured by microarray analysis in PBMCs of untreated secondary syphilis patients and healthy controls. Weighted Gene Coexpression Network Analysis (WGCNA) was used to construct the expression of miRNAs and the clinical data of secondary syphilis patients. Gene ontology (GO) and KEGG enrichment analyses were performed on target genes of miR-142-3p. Results. 244 miRNAs exhibited at least 1.0-fold differential expression between secondary syphilis patients and healthy controls. The miRNAs were divided into three modules by WGCNA. The blue module was positively correlated with TPHA, TRUST, duration of disease, and erythema. And in the blue module, the expression of miR-142-3p was significantly higher in secondary syphilis patients than in healthy controls (p=0.02), which is also close to the clinical features of secondary syphilis. GO and KEGG pathway analyses showed that these target genes of miR-142-3p are correlated with endocytosis and positive regulation of the apoptotic process. Conclusion. The elevated miR-142-3p expression in PBMCs may play an important role in the immune response to T. pallidum infection and may be a potential biomarker for secondary syphilis.