It is beneficial to a person’s physical and mental health to engage in regular physical activity, while public parks are a critical infrastructure for encouraging physical activity. However, little research has examined how parks’ and users’ characteristics affect activity intensity. Using primary data collected from 432 users of six public parks of different sizes in Bangkok, this study examined the relationship between park and user characteristics and moderate-to-vigorous physical activity (MVPA). Descriptive and inferential statistics were used to understand the user profile and usage of the parks. Logistic regression was employed to determine the association between MVPA and the characteristics of parks and park users. The results show that MVPA was positively influenced by gender (being male with MVPA of 29.0%), time spent in the parks (MVPA of 22.7%), weekend evenings by 21.6%, large park size by 18.9%, and availability of park facilities by 233.0%. However, age, marital status, and occupation did not influence MVPA. Our findings indicate that the improvement of park facilities and enlargement of park size can increase MVPA for various ages and genders. Furthermore, improving facilities in small parks, raising local awareness, and disseminating information about parks can boost MVPA.