Borderline personality disorder (BPD) is associated with significant interpersonal dysfunction and risk of suicidal ideation (SI). One mechanism underlying interpersonal problems in BPD is deficits in social problem-solving (SPS). Using ecological momentary assessment (EMA), this study investigated how acute interpersonal problems (conflict, isolation, low support, rejection) were associated with daily SI in adolescents with BPD features. A community sample of 21 adolescents aged 13-19 years (Mage = 16.98, SD = 1.19) were recruited. The sample was predominantly female (n = 7, 50%), bisexual (n = 8, 38.10%), and White (n = 14, 67%; n = 3 Black; n = 1 Asian; n = 3 mixed race). Twelve participants (57.14%) reported a prior suicide attempt and nineteen (90.48%) reported self-injury. Participants completed the Social Problem-Solving Inventory-Revised (D’Zurilla, 2002), Means-End Problem-Solving Procedure (Linehan et al., 2005), and demographic questionnaire via Qualtrics. Approximately 63% of the variability in SI was due to within-person (versus between-person) variance. We observed high degrees of variability in interpersonal variables and SI. EMA results suggested daily perceived rejection (? = 0.09, SE = 0.02, p < .001), isolation (? = 0.05, SE = 0.01, p = .005), and conflict (? = 0.65, SE = 0.30, p < .001) were associated with SI concurrently. Increased isolation predicted SI prospectively (? = 6.07, SE = 1.30, p = .03). Self-reported SPS was a significant moderator of the effects of isolation. Those with weaker SPS abilities were more likely to experience SI in response to feeling isolated (? = - 0.01, SE = 0.02, p = .03). Adolescents who felt rejected, isolated, and experienced a conflict were more likely to simultaneously endorse SI. Those who felt isolated were especially likely to endorse SI at the next time point. These results align with prior research demonstrating interpersonal problems proximally increase risk for suicidality. Our findings also suggest that those with fewer SPS skills may have a harder time managing distress when feeling isolated from others. Developing this skillset may be an important clinical target for preventing escalations in suicide risk—particularly among those vulnerable to interpersonal strife, such as youth with BPD features. This study adds to the literature on advancing near-term prediction of SI, and highlights a potentially modifiable interpersonal skill that is relevant for suicide risk.