Health misinformation has become a salient issue on social media. To lower the risk of health misinformation, fact-checking matters. However, most existing studies investigated fact-checking from the journalism angle, while little is known about how information-seekers’ social media use affects their fact-checking behaviors. Also, it remains unclear how individuals’ health worry is associated with health fact-checking. Based on the O-S-O-R model, this study explored the underlying mechanism through which health worry and social media might hinder users’ fact-checking. Specifically, with a two-wave panel survey conducted in China during the COVID-19 pandemic, this study showed that individuals’ worry about COVID-19 increased social media information overload, which resulted in social media fatigue that could reduce health fact-checking. Also, the direct relationship between worry and fact-checking was not significant, but was completely mediated by social media information overload and social media fatigue. The findings demonstrate the negative roles of worry and social media in inhibiting users’ fact-checking behaviors. Important theoretical and practical implications for promoting effective fact-checking are discussed.