OBJECTIVES: To conduct a cost-utility analysis of rotavirus vaccine (Rotarix®) for infants in Japan. METHODS: A Markov model was constructed to analyze costs and Quality-Adjusted Life Years (QALYs) from the societal perspective. We captured costs and outcomes until infants reached five years old. In the Markov model, one month was set as one cycle. Both costs and utility were discounted at 3 percent annually. Based on suggestions from expert of pediatric infectious diseases, various factors have relationship with immunological status, such as breastfeeding and communal living, were adopted to our model. The healthcare cost were derived from Japanese data. Effectiveness of vaccination was derived from clinical trial in Europe. Various sensitivity analyses, both univariate and probabilistic ones, were conducted. We used QALY for outcome measurement. Quality weight for each status was derived from the foreign literature. RESULTS: In the basecase analysis, Rotarix® increased both costs and QALYs, compared to no vaccination. Rotarix® would increase costs of JPY 9253 (US$93, USD1=JPY100). and increase 0.0024 QALY in infants in Japan. ICER for Rotarix was JPY3.8million (US$D38,000) per QALY gained. Sensitivity analyses suggested the robustness of the results. When we set threshold for 1QALY to JPY5.0million (US$50,000), the probability of the acceptance of Rotarix was 83%. CONCLUSIONS: Rotarix® for infants in Japan, is thought to be cost-effective.