Abstract： Objective To investigate the potential role of exosomal microRNA-451a(miR-451a)derived from serum in early diagnosis and treatment of colorectal cancer(CRC).Methods MiRNA microarry was per-formed to detect the miRNAs differently expressed between preoperative and postoperative serum exosomes derived from CRC patients.TCGA databases was used to analyze the expression levels of miR-451a in CRC tissues samples,and the correlation between miR-451a expression level and clinicopathological indices was an-alyzed.The area under receiver operating characteristic(ROC)curve(AUC)was used to analyze the diagnos-tic efficacy of miR-451a in rectal cancer and colon cancer,respectively.The target genes of miR-451a with en-riched pathways were analyzed by using bioinformatics software.Results The high expression level of miR-451a was negatively correlated with distant metastasis in rectal cancer patients(P=0.032,r=-0.179).The expression level of miR-451a had a good diagnostic capability in CRC tissues(P＜0.01).Enrichment analyses revealed that the target genes of miR-451a were closely related to several important pathways in the occur-rence and development of CRC.Conclusion Exosomes miR-451a might be a potential biomarker for the early diagnosis and treatment of CRC.