Purpose Declining birth rates are an important social issue worldwide, and allocating resources to benefits for child-rearing households is a necessary countermeasure. In this study, we investigate and compare the relationship between child-related social security costs and total fertility rate internationally.Method In 2011, the ratios of family- and elderly-related social spending to gross domestic product (GDP) were recorded in 34 Organisation for Economic Co-operation and Development (OECD) member countries. The former was designated as the percentage allocated to members of the population between the ages of 0 and 14 (young population ratio), and the latter was designated as the percentage allocated to members of the population over the age of 65 (elderly population ratio). We compared these two factors for every country and performed correlation and partial correlation analyses of total fertility rates and family-related social spending to GDP adjusted by population proportion to examine the relationship between the two.Results The comparison of the youth and elderly populations' spending ratios in the total social spending to GDP ratio revealed that OECD countries had an average family-related social spending ratio of 0.13 and an average elderly-related social spending ratio of 0.47. Comparatively, Japan has a family-related social spending ratio of 0.10 and an elderly-related social spending ratio of 0.45. In the correlation analysis for total fertility rates and family-related social spending to GDP ratio, the benefits-in-kind to GDP ratio and total fertility rates indicated a trend toward correlation (r=0.32, P=0.06). In addition, the results for the partial correlation between family-related social spending to GDP ratio and total fertility rates showed a significant correlation between the two. When divided into cash benefits and benefits-in-kind, the partial correlation analysis of the GDP ratios and total fertility rates revealed a significant correlation (r=0.51, P<0.01). Benefits-in-kind (r=0.45, P<0.01) had a stronger correlation than did cash benefits (r=0.39, P=0.03).Conclusion In an international comparison accounting for economic standards, the social security cost of children and child-rearing families in Japan was low. Further, in terms of social security spending, increasing benefits-in-kind, such as improving childcare services or preschool education, is one factor that improves the total fertility rate.