Purpose: This secondary data analysis study examined the level and network of obesity-related health behaviors among young adult men and women. Methods: The study included 1,754 adults (802 men and 952 women) aged 19–44 years who participated in the 8th 3rd Korea National Health and Nutrition Examination Survey (2021). The selected obesity-related health behaviors included alcohol abstinence, not smoking, proper sleep, eating breakfast, fruit intake, vegetable intake, not eating out, aerobic physical activity, walking, and weight training. Obesity-related health behavior networks were analyzed for density, inclusiveness, degree, and degree/closeness/betweenness centrality using social network analysis. Results: The results showed that obesity among all participants was 36.2%, with a higher prevalence in men (70.4%) than in women. Women had higher levels of health behaviors related to alcohol abstinence, not smoking, and diet; however, they had lower levels of health behaviors related to physical activity. In the obesity-related health behavior network, non-obese women showed a very high density and average degree, indicating high levels of concurrent health behaviors. In contrast, obese women exhibited very low density and average degree, indicating low levels of concurrent health behaviors. The obesity-related health behavior networks of non-obese and obese men had similar densities, average degrees, and network structures. Furthermore, they exhibited a high centrality of vegetable intake, proper sleep, aerobic physical activity, and walking. Conclusion: Efficient obesity management can be achieved by focusing on health behaviors with high centrality in the health behavior network and differentiating approaches according to sex.