Abstract: Rural residents are the main participants in household waste classification. Their willingness and behaviors directly affect the efficiency of waste classification management, as well as the success or failure of scenic countryside construction. Based on a survey data of rural residents in the Taihu Lake Basin, this paper analyzed the impacts of social capital on rural residents' domestic waste classification and its mechanism by the Ordered Probit model and the OLS model. Results show that currently, the social capital scores of rural residents in the Taihu Lake Basin vary across different dimensions. In terms of household waste classification, 88.6% of the residents surveyed are willing to classify. However, there are still some surveyed residents who are willing to classify without actual behaviors. Social capital of different dimensions, such as social network, social trust, and social norms, positively influences the willingness of rural residents to sort household waste and their related behaviors. In terms of mechanism, social capital has effectively promoted rural residents' willingness and waste sorting behaviors by enhancing their awareness of the classification categories of domestic waste and their corresponding responsibilities. In terms of heterogeneity, the role of social capital in each dimension varies in a group with diverse demographics such as age, educational background, and income. Consequently, to effectively encourage rural residents' participation in domestic waste classification, this paper suggests: to strengthen network construction of rural grass-roots organizations, to establish a sense of responsibility for the household waste classification and a group supervision mechanism, to promote the accumulation of social capital in a muti-dimensional and well-rounded way, and to form a classified treatment system for household waste according to local conditions.