Background <p>Biliary atresia (BA) is a serious condition and the leading cause for liver transplantation in children. The exact cause for BA is currently unknown, with one suggested mechanism being a viral infection. Cytomegalovirus (CMV) is the most common viral infection in BA patients and was previously known to be associated with worse outcomes, including liver fibrosis. Our study aimed at investigating the association between CMV infection and liver fibrosis in BA patients who underwent the Kasai procedure at our institution.</p> Methods <p>This study was a retrospective analysis of medical records from BA patients who underwent the Kasai procedure between January 2019 and July 2024 at our hospital.</p> Results <p>Our study involved 15 male and 23 female BA patients. The proportion of CMV-infected patients (<i>n</i> = 11) was lower than that of the non-CMV-infected BA patients (<i>n</i> = 27). The association between CMV infection status and liver cirrhosis (<i>p</i> = 1.0) was statistically insignificant. However, the age at the Kasai procedure showed a statistically significant association with cirrhosis (<i>p</i> = 0.027; odds ratio [OR] = 7.20; 95% confidence interval [CI] = 1.27–40.7). Moreover, a multi-variate analysis revealed a strong association between the age at the Kasai procedure and liver cirrhosis (<i>p</i> = 0.029; OR = 7.37; 95% CI = 1.22–44.42).</p> Conclusion <p>Our study’s findings suggest that CMV infection might not significantly affect the degree of liver fibrosis in BA patients following the Kasai procedure. Furthermore, the age at which the Kasai procedure is performed might influence the development of liver cirrhosis in these patients. These insights could reshape our understanding of BA and guide future research and clinical practice.</p> Graphical Abstract <p></p>