There is a significant body of research linking empathy with prosocial behaviors e.g., (Ruci et al., 2018). Previous research has explored the impact of sibling relationships on prosocial behavior during childhood (Beffel et al., 2022), however, few studies have systematically examined the enduring effect of sibling relationship quality on feelings of empathy and prosocial tendencies into adulthood (Van der Graaff et al., 2018). Gilligan et al. (2024) is a notable exception that documents a positive relation between the quality of adult sibling relationships and empathy. This suggests that adults with high quality sibling relationships embody more prosocial attitudes. The purpose of the current study is to add to the literature documenting the continued positive impact of adult sibling relationship quality on empathy and prosociality, by examining both traditional kinship and complex relationships. The current study will also explore how Appalachian identity impacts the quality of adult sibling relationships. Consistent with previous research (Lin et al., 2024), it is expected that total scores on the Lifespan Sibling Relationship Quality Scale (LSRS; Riggio, 2000) will account for unique variance in prosocial behavior (PTM; Carlo & Randall, 2002) beyond that explained by scores on the Empathy Assessment Scale (EAS; Malakciouglu, 2022). This will be tested using multiple linear regression modeling. Further, it is expected that Appalachians will report higher scores on all outcome variables (i.e., LSRS, EAS, and PTM scores). Independent samples t-tests will be used to examine mean differences. Data from this study can be used to inform interventions across the lifespan, relevant to different types of sibling relationships (i.e., biological, step, etc.) and sensitive to cultural differences (i.e., regional identity). Data will be collected anonymously using Qualtrics though email and social media ads. Data collection will be completed by the end of February.