Objective: Sexual and gender minority people of color (SGM-POC) experience intersectional forms of minority stress, including heterosexism within racial/ethnic minority communities, which can contribute to feelings of conflict between SGM and racial/ethnic identities. Internalized stigma may be a consequence of sexual orientation-based discrimination but has not been tested as a mechanism linking intersectional minority stress to identity conflict among SGM-POC. We hypothesized that the association between experiences of heterosexism in racial/ethnic minority communities and identity conflict would be mediated by internalized stigma among SGM assigned female at birth (SGM-AFAB). Method: Participants were 316 SGM-AFAB who identified as POC. Data were collected as a part of an ongoing longitudinal cohort study of young SGM-AFAB. We tested the longitudinal mediation using data from baseline, 6-month follow-up, and 1-year follow-up assessments. Results: Internalized stigma at 6-month follow-up partially mediated the association between experiences of heterosexism in racial/ethnic minority communities at baseline and identity conflict at 1-year follow-up. Conclusions: For SGM-POC, experiences of heterosexism within their racial/ethnic communities may lead to internalization of those negative attitudes. A consequence of internalizing heterosexist attitudes from one's racial/ethnic group could be a feeling that one's sexual orientation and racial/ethnic identities must remain separate, perhaps to maintain connection to one's racial/ethnic community. Identifying internalized stigma as a mediating process is critical to better understand identity development for SGM-POC, and has important clinical implications for working with this population. (PsycInfo Database Record (c) 2021 APA, all rights reserved).