The purpose of this study was to investigate the motivation of research mentors to address race/ethnicity in their research mentoring relationships, using self-determination theory as a conceptual framework. Mentors from STEM fields primarily in the biological sciences (N = 115) were asked to report their level of motivation and the reasons behind their motivation to address the role of race and ethnicity in their mentoring relationships. Mentors' responses were coded using a qualitative approach, and results were examined by mentors' degree of motivation, previous experience with mentoring trainees from different racial/ethnic groups, and mentor race/ethnicity. Extrinsic motivation and amotivation were the most frequently assigned codes to mentors' responses. Implications of these findings for mentor practices, higher education initiatives, and for diversifying the STEM workforce are discussed.