This study aimed to assess the fertility knowledge of Japanese education undergraduates who plan to become schoolteachers and examine related factors. A cross-sectional questionnaire survey was conducted with 252 first-year education undergraduates at a Japanese university. The Cardiff Fertility Knowledge Scale (CFKS) was used to measure fertility knowledge, and other items inquiring about basic reproductive knowledge were included. We assessed the relationship between fertility knowledge and gender and the experience of future life planning, among other factors. We found that fertility knowledge varied. Participants possessed a relatively good knowledge of the relationships between fertility and female ageing, and smoking, but limited knowledge about the effect of sexually transmitted infections on fertility. Male participants answered more correctly than female participants (p < 0.01) regarding 'sperm production'; however, female respondents answered more accurately than male respondents (p < 0.01) regarding 'timing of menopause. In Japan, the national curriculum standard for upper secondary schools was revised in 2018, and fertility was added to the Health and Physical Education curriculum. The study results suggested that it is important to include fertility in a sex education teaching curriculum for education undergraduates to enable them to deliver fertility education as teachers in the future.