The study aims to explore the effect of security on social trust and the roles of life satisfaction and ostracism among Chinese adults. Toward this end, the study recruited 1,206 Chinese adults to complete the Security Questionnaire, Social Trust Questionnaire, Satisfaction with Life Scale, and Ostracism Experiences Scale. Results show that (a) security is positively correlated with social trust among Chinese adults, (b) life satisfaction partially mediates the effect of security on social trust, and (c) ostracism moderates the relationship between security and social trust. Furthermore, findings indicate that security can directly predict social trust as well as indirectly predict social trust through life satisfaction for adults in China. Security has a strong predictive effect on social trust - especially for individuals with low levels of ostracism.