Abstract: MicroRNAs (miRNAs) play important regulatory roles in mammalian cells and viral replication. Let-7 family of microRNA are important regulators in cell differentiation, human cancer and virus infection. The aim of the present study was to investigated miRNA which involved in Classical Swine Fever Virus (CSFV) infected Swine Umbilical Vein Endothelial Cells (SUVECs). Software predicting analysis was performed to screen out the potential miRNA. Four members of let-7 family, let-7a, let-7c, let-7f and let-7i were screened out as candidates. Luciferase activity assay showed that let-7a, let-7c and let-7i could bind to the 3' untranslated regions (3' UTR) of CSFV. Taqman qRT-PCR analyse showed that the inhibition or overexpression of let-7a and let-7c influenced the replication of CSFV. Mimics of let-7a and let-7c could significantly down-regulate CSFV replication. Further study showed that the expression of let-7a and let-7c were down-regulated in the CSFV infected cells and heterogeneous nuclear ribonucleoprotein A1( hnRNP A1), a negative regulator of let-7a, was up-regulated. The results indicated let-7a and let-7c could inhibit viral replication and the CSFV induced negative feedback regulation to interfere with let-7a expression. This study firstly suggested that miRNAs let-7a and let-7c play important roles in the replication of CSFV. These findings provide novel information on the interaction of miRNAs and the replication of CSFV.