The object of this study was to evaluate Japanese encephalitis virus (JEV) antibody titer changes in broodmares and foals. Antibodies of 112 sera were detected by applying hemagglutination inhibition test. To the best of our knowledge, this is the first report that compares antibody titers of foals to that of their dams in order for evaluate optimal time of JEV vaccination. Most mares` antibody titers were variable. However, the highest titers in foals presented in their first month, and antibodies titers in all foals decreased gradually over time. This study provides important benchmarks that can be used to select optimum time JEV of vaccination.