Biliary atresia (BA) is a pediatric liver disease characterized by fibro-obliteration and obstruction of the extrahepatic biliary system, that invariably leads to cirrhosis and even death, if left untreated for extended time. However, its pathology and etiology still remained unknown. In this study, we tested the expression of adducin 3 (ADD3), the gene identified as a susceptibility gene in BA by GWAS, and uncovered its upstream regulatory microRNA in the pathogenesis of BA. In this study, 14 infants with BA and 14 infants with choledochal cyst (CC) were enrolled as experimental group and control group, respectively. ADD3 and microRNA-145 (miR-145) expression profiles in liver tissues of BA and CC were determined using qPCR. Luciferase reporter assay was performed to verify the direct interaction between miR-145-5p and ADD3 3' Untranslated Regions (3'UTR). The Lentiviral vectors containing miR-145, miR-145-3p inhibitor, miR-145-5p inhibitor, empty vector were transfected into human hepatic stellate cell line (LX-2) to determine the functional effect of miR-145 on ADD3 expression at both mRNA and protein level. MiR-145 was shown to be down-regulated in liver tissues of infants with BA compared to CC (p = 0.0267). ADD3, verified as a target of miR-145-5p, was shown to be overexpressed in infants with BA at the mRNA level (p = 0.0118). Transfection of lentiviruses containing miR-145 into LX-2 cells decreased the expression of ADD3 at both mRNA and protein level compared to negative control group, and suppressed the expression of p-Akt at protein level. Our study has shown that overexpressed ADD3 and downregulated miR-145 were detected in BA liver tissues. MiR-145-5p was confirmed to target ADD3 by luciferase reporter assay. The downregulation of miR-145 may contribute to liver fibrosis in BA by upregulating the expression of ADD3.