BACKGROUND: Congenital cytomegalovirus (CMV) disease, a common mother-to-child infection, can lead to neurological sequelae. Some clinical trials have shown that oral valganciclovir (VGCV) can improve hearing and neurodevelopmental impairment in infants with congenital CMV disease. However, VGCV has neither been approved in Japan nor other countries as a treatment for this disease by the government health insurance. METHODS: This study is a non-randomized, prospective, open-label, multicenter, single-arm clinical trial and will include subjects meeting the following criteria: confirmation of positive CMV-DNA amplification in urine by an in vitro diagnostic test within 21 days of age; congenital CMV disease with one or more central nervous system disorders-microcephaly, hydrocephalus or ventricular enlargement, periventricular calcification, cortical hypoplasia or white matter injury, retinal choroiditis, and abnormal auditory brainstem response (ABR); and infants within 2 months of age with a gestational age ≥32 weeks at birth and weighing ≥1800 g at the time of registration. Subjects will be orally administered 16 mg/kg VGCV twice daily for 6 months. The target number of cases for enrollment between February 3, 2020 and July 31, 2021 is 25. Primary endpoint is the change in whole blood CMV loads before and after 6 months of treatment. The important secondary endpoint is the change in ABR (both best and total ear hearing assessments) before and after 6 months of treatment. The safety endpoints are adverse events and drug side effects. DISCUSSION: To the best of our knowledge, this multicenter, open-label, single-arm study will be the first well-designed clinical trial to evaluate the efficacy of oral VGCV in infants with congenital CMV diseases. The findings will reveal the efficacy and safety of oral VGCV treatments and enable the approval of oral VGCV as a treatment for infants with congenital CMV disease by the government health insurance of Japan.