Introduction: This study aims to explore experiences of romantic relationships and to examine determinants of desires to marry and have children in the future among Japanese university students. Methods: A cross-sectional study was conducted among undergraduate students of A University, located in the capital city of a Japanese prefecture, using an anonymous self-administered and structured questionnaire developed by an online survey software. Results: A total of 815 respondents with complete data were analyzed by logistic regression analysis. Over 80% of males and females expressed the desire to marry and have children in the future. It was found that for both female and male respondents, the "desire to marry" was associated with currently being in a romantic relationship or having experience of sexual intercourse. On the contrary, the "desire to have children" was associated with currently being in a romantic relationship or having experience of sexual intercourse only among male respondents, and no significant association was observed among female respondents. Conclusion: "Currently being in a romantic relationship" and "having experience of sexual intercourse" were associated with wanting to marry and have children in the future among male university students. This suggests that these may be important factors in providing a positive perception regarding having children when they attain childbearing age.