The aim of this study was to examine how mentors provide social capital to Latinx adolescents in science education. Participants were drawn from a long-term, comprehensive science support program at a medical university in the Midwest. Using a case study approach, various stakeholders participated in one-on-one, in-depth qualitative interviews: 11 Latinx high school and college students, three staff members, 12 graduate student mentors, and 13 faculty mentors. Protocols were approved by an Institutional Review Board. The qualitative analysis was guided by a modified grounded theory approach, which involved three steps: initial coding, focused coding, and modified axial coding. Participants described how mentors promoted youth's social capital through bridging and bonding behaviors, which were related to students' (a) enhanced professional development, (b) broadened perspectives about science specifically and education broadly, (c) exploration opportunities, and (d) increased interest in science. This study fills gaps in the literature by showing how bridging and bonding social capital are provided in mentoring relationships and by examining STEM mentoring in a Latinx adolescent sample. Study findings have implications for increasing Latinx students in the science education pipeline. Future directions for research on STEM mentoring and social capital are discussed.