Research in the sociology of education has long stressed the benefits of social capital for academic success. This explanation, however, offers little insight for understanding the academic success of underrepresented students, including Latinos and African Americans – who are often examined through deficit models. Drawing from social capital theory, this study examines the effect of an additional source of social capital that may facilitate college success for underrepresented students: sibling social capital. I expect that having an older sibling who attended college and talking to them about educational matters will prove especially beneficial for underrepresented students’ college achievement (college GPA) and engagement (academic interactions) compared to their overrepresented peers (whites and Asians). Using the Social Interactions and Academic Opportunities Survey, with a random sample of 401 undergraduates attending a Hispanic Serving Institution, I use OLS and logistic regression to predict college success. I measure sibling social capital in two ways: 1) number of older sibling who attend/attended college and 2) the frequency and topics of educationally relevant conversations the younger sibling reports having with their older sibling while in college. Results indicate that sibling college attendance has positive effects for underrepresented students compared to overrepresented groups. The effect of educationally relevant conversations is mixed. Analysis focused on typically marginalized students may reveal tools for success that have been previously overlooked by social capital studies and studies on the academic achievement of underrepresented groups.