Based on a 1998 survey of urban residents in four Chinese cities, this article presents a rationalist interpretation about the determinants of social trust .It first breaks trust into four categories, namely , trust in family members, trust in friends, trust in acquaintances, and trust in strangers, the last of which is called “social trust” .After reviewing the existing theories of social trust, the second section puts forward a hypothesis that the more resources one possesses, the more likely s he trusts others .This is so because when one owns more resources, her his “disaster threshold” would be higher and s he would be less vulnerable to potential losses due to others' untrustworthiness .The final section finds empirical evidence to support this rationalist interpretation .