Abstract Haze has become one of the most life-threatening problems in China. Chinese people become more dependent on receiving health information from social media, especially WeChat, which shapes their health perceptions and behaviors. Despite the prevalence of health information-seeking behavior (HISB) on WeChat, the predicting factors and consequences of Chinese people’s haze HISB using WeChat remain unclear. To fill this gap, a hypothesized model was proposed under the risk perception attitude framework and tested with a longitudinal web-based survey of Chinese people residing in Mainland China, to understand the antecedents and behavioral outcomes of HISB on WeChat. The results from the structural equation modeling showed that perceived risk significantly predicted haze HISB on WeChat, which predicted the intention of wearing PM2.5 mask but not reducing outdoor exercises. The efficacy beliefs of both protective behaviors were not significant predictor of haze HISB. Theoretical and practical implications were discussed.