The purpose of this study was to examine how college students’ interpersonal attribution for their success was affected by the type of achievements and the characteristics of the interpersonal relationship as well as their modesty orientation. Two hundred undergraduate students participated in this study and 192 valid questionnaires were collected. Adopting scenario experimental method, this study manipulated the variables of “threat of successful event” and “closeness to the interacting target” in an achievement of horizontal distinctiveness. The dependent variables were participants’ choice of attributional reason and motivation, in addition, their modesty scores were measured as well. The results of χ 2 analyses showed that when the success was a threat to the interacting target, participants would attribute their success to “luck” with a motivation of “empathy”. When the achievement was not a threat, participants would attribute their success to “effort” and “ability” with intimates with a motivation of “sharing glory”, but to ”luck” with acquaintances with motivation of “obeying social modest norm”. Moreover, the results of t-test revealed that when the success was not a threat to the intimate, the modesty orientation scores of those who attributed their success to external factors were significantly higher than those who attributed their success to internal factors.