The aim of this study was to clarify the associations of family members living together with healthrelated behaviors in Japanese young workers. The participants were 300 men and women aged 20-39 years in 2015 who had a job. A web-based self-administered questionnaire on status of partnering and parenting, number of family members living together, dietary habits, drinking habit, smoking habit, self-rated health, employment status, working time and commuting time was conducted through Internet. Multiple logistic regression analysis and general linear models were used to assess the association of family members living together with healthrelated behaviors. The multivariate-adjusted odds ratio (95% confidence interval, p-value) for current drinking in unmarried participants living with their parents compared to unmarried participants living alone was 0.35 (0.13-0.93, p=0.036). The adjusted means of frequency of breakfast skipping and frequency of eating out showed a trend for inverse associations with the presence of a partner and children. However, those associations disappeared after adjustment for age of youngest child. The findings suggest that the presence of parents might affect drinking behavior and that age of youngest child living together might affect the frequency of breakfast skipping in young Japanese workers. J. Med. Invest. 66 : 141-147, February, 2019.