Abstract Purpose: To explore the linguistic elements of engagement and tone used by parents of children with cancer and a patient navigator (PN) during a pilot study of a health insurance literacy (HIL) intervention. Methods: A trained PN delivered a four-session Zoom-based HIL intervention for parents of children with cancer that contained content on: Session 1 (S1) health insurance terms, (S2) using health insurance, (S3) insurance appeals/legislation, and (S4) budgeting and financial strategies. We applied Linguistic Inquiry Word Count (LIWC-22) software to analyze transcriptions of each session regarding engagement and tone. We report, in aggregate, differences in language: analytical language (e.g., formal, logical), clout language (e.g., confidence, leadership), authenticity language (e.g., degree of self-monitoring), and emotional tone (e.g., positive and negative emotion words) (all range 1-99) between S1 and S4 using paired t-tests. We also analyzed language similarities between the PN and the parent using Language Style Matching, which represents the degree to which both speakers are engaged in the conversation. Results: Of 10 participants, 9 completed 4 sessions, and 1 parent completed 3 (39 sessions total); sessions were on average 35.1 (SD=6.4) minutes. Most participants were women (80%), married (90%), white (100%), and non-Hispanic (90%); half had a college degree. The PN spoke more than parents across all four sessions (90% PN vs 8.8% parent); however, parent engagement, as represented by word count, increased as the sessions went on (mean S1: 414 words, S4: 603.8 words, p=0.21). S1 contained the most language exchange between parents and the PN (median word count: 5,533.5). The discussions became increasingly authentic (mean by session: S1:24.2; S4:28.6; p=0.02), held more clout (S1:77.8, S4: 85.8; p=0.009), and increased in emotional tone (S1:49; S4:65, p=0.002). Analytical language decreased over time (S1:24.4; S4:19.8, p=0.05). Language style matching was consistently high and trending upward across sessions (S1:0.80; S4: 0.81, p=0.3). Conclusions: In a pilot test of a HIL intervention, we saw an increase in authentic language, emotional tone, and parent word count coupled with a decrease in analytical language, indicating increased rapport between the PN and parent over the sessions. This suggests there is emotional and supportive value in PN-led interventions as compared to self-directed interventions. PNs can build trust and promote equity by deconstructing and personalizing health insurance information. Future work should explore how rapport built between parents and PNs relates to health insurance literacy and financial toxicity outcomes. Citation Format: Mary K. Killela, Anne C. Kirchhoff, Perla Vaca Lopez, Amy Chevrier, Monique Stefanou, Katie Rogers, Douglas Fair, Echo L. Warner. Building rapport in navigator-delivered health insurance literacy interventions: Engagement and tone used by parents of children with cancer and patient navigators [abstract]. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr B049.