<p>A growing body of literature has confirmed the within-person process from interpersonal conflict to adolescent mood on a day-to-day timescale. However, research on how, when and for whom adolescent interpersonal conflict relates to their daily mood is underdeveloped. This study examined whether interpersonal conflict is related to mood through threat appraisal and self-blaming attribution and whether these relationships would be moderated by daily social support and psychological capital. Daily experience-sampling data were collected over 14 consecutive days from 264 Chinese adolescents (<i>M</i>_age = 14.74 years, <i>SD</i> = 1.48). The results indicate that adolescents had more negative moods and less positive moods on the days when they experienced more conflicts than usual. Same-day threat appraisal serves as a mediator in the relationship between interpersonal conflicts and negative mood, and same-day threat appraisal and self-blaming attributions play serial mediating roles in the relationship between interpersonal conflicts and same-day positive mood. Furthermore, the relationship between interpersonal conflict and same-day positive mood was moderated by daily social support and psychological capital, i.e., this relationship was stronger in days with more social support and in adolescents with high levels of psychological capital, which is consistent with the reverse stress-buffer model. These findings reveal the instant cognitive mechanism of interpersonal conflict and daily mood and identify when and for whom interpersonal conflict is associated with daily mood.</p>