["Applied Psychology: Health and Well-Being, Volume 18, Issue 3, June 2026. ", "\nAbstract\nHealthy ageing is a major public health challenge in rapidly ageing societies, where longer life expectancy does not always translate into sustained well‐being. This study examines health trajectories among Chinese middle‐aged and older adults, focusing on social participation and the mediating role of life satisfaction. Using four waves (2011–2018) of the China Health and Retirement Longitudinal Study, we applied latent growth curve modelling to assess overall change and individual heterogeneity and latent growth mixture modelling to identify five trajectory categories across six dimensions: environment, vitality, cognitive function, sensory and physical abilities, daily activities and psychological well‐being. The five classes were high initial stable, high initial declining, moderate initial increasing, moderate initial declining and low initial increasing. Multinomial logistic regression showed that greater social participation was associated with a lower likelihood of less favourable trajectories; relative to high initial stable, the low initial increasing group exhibited a significantly reduced risk. Cultural and recreational activities showed the strongest protective association, whereas volunteer service had no significant impact. Life satisfaction partially mediated the association between social participation and trajectory membership. These results suggest that expanding meaningful social participation and improving life satisfaction are important pathways for promoting healthy ageing among Chinese middle‐aged and older adults.\n"]