This case study investigated how mentors and mentees in biology experience and understand race and ethnicity in their research mentoring relationships. Semistructured interviews were conducted with mentors (n = 23) and mentees (n = 15) who had participated in an undergraduate biology summer research opportunity program at a large Midwestern research-intensive university. Interview transcripts were coded using an inductive, thematic analysis. Themes that emerged are presented, describing both participants' experiences with and beliefs about race and ethnicity in research training contexts (e.g., mentoring relationships, lab and field experiences). Although similarities were identified, the experiences and beliefs of mentors and mentees were not always aligned. Implications of the findings for training interventions and institutional partnerships to enhance the effectiveness of research mentoring relationships are discussed, with the goal of positively impacting the educational success of students from historically underrepresented racial/ethnic groups in science career pathways.