Purpose To investigate the associations between beliefs of thinness, and body image as well as weight control methods among internet users. Methods The study invited users on the internet to fill in an internet questionnaire. There were 1089 users (21.4% male, 78.6% female) completing the questionnaire. The link for answering the questionnaire was disseminated through many internet channels, including Bulletin Board System, emails, internet communities, and instant message software. The beliefs of thinness was measured by 20 items (total score ranged from 20 to 100) which was designed based on the previous studies, and contained two sub-scales (media effects and benefits of thinness). Body image included two sub-scales, namely the level of body dissatisfaction and perceived negative body evaluation. Weight control methods included healthy eating regulation, unhealthy eating regulation, increasing energy expenditure, and adopting external forces for losing weight. Multiple linear regressions were conducted to investigate the associations. Results After controlling for age, sex, education level, occupation, and residential area, beliefs of thinness is significantly and positively associated with body dissatisfaction, perceived negative body evaluation, the level of healthy eating regulation, the level of unhealthy eating regulation and the level of adopting external forces for losing weight. There exists no significant association between beliefs of thinness and the level of increasing energy expenditure. Conclusion The beliefs of thinness are widespread in the internet media. People who deeply belief that â€œthinness is beautifulâ€ could increase the dissatisfaction of body image and conducting health harmful weight control methods. Keywords Health-related behaviors, communication/social media, health promotion Key messages 1. The beliefs of thinness widespread in the internet media. 2. The beliefs of thinness is positively associated with dissatisfaction of body image and health harmful weight control methods. 3. The beliefs of thinness is not associated with increasing energy expenditure.