Otitis media, one of the most common childhood diseases, is characterized by in ammation or infection of the middle ear. Due to their ease of access, daily probiotics are recommended for the prevention of early childhood otitis media. This study aimed to assess the impact of probiotics on the incidence of otitis media using a dataset (n = 95,380) from the Japan Environment and Children's Study, a nationwide birth cohort study. After multiple imputations, the association between the incidence of otitis media in early childhood and the daily frequency of yogurt intake in children and mothers was examined using a generalized linear model with adjusting for several confounders. Repeated incidence of otitis media during the two years after birth was found in 14,874 participants (15.6%). Based on participants with the lowest frequency of yogurt intake ("almost never") as the reference group, risk ratios (95% con dence interval) for otitis media incidence decreased with higher frequencies of yogurt intake in children at one year of age, but also independently in mothers during pregnancy. Furthermore, although not statistically signi cant, a similar association was observed in the subgroup of those with cleft lip and/or palate (CL/P), a high risk group for severe otitis media. Thus, increased regular yogurt intake in both children and mothers was associated with a decrease in early childhood otitis media.c Additionally adjusted for the other daily frequency of yogurt intake in children or in mothers with Model 2.