Abstract Excellent mentorship is critical to the career success of clinical and translational scientists. As such, the CTSA K12 program is aptly named the Mentored Research Career Development Award Program in Clinical and Translational Science. K12 Scholars generally have a team of mentors comprised of content experts, methodologists, and career development advisors. The new CTSA K12 funding opportunity announcement (PAR-21-336) also requires each Scholar’s mentoring team to include a clinician, and for Scholars planning to lead or gain experience in clinical trials, a clinical trialist mentor. As with the other components of the CTSA grant, the K12 also emphasizes diversity, equity, inclusion, and accessibility (DEIA). Evidence-based mentor training for clinical and translational scientists is available and widely used, including at our University of Texas Health Science Center at San Antonio (UTHSCSA) CTSA hub, yet no such training exists for non-researcher clinicians interested in co-mentoring researchers. The aim of this administrative supplement is to 1) develop, 2) implement, and 3) evaluate a short mentor training workshop for clinicians and clinical trialists at UTHSCSA and its CTSA partner, UT Austin, and then to disseminate the training program throughout the CTSA Consortium. Experts in mentorship training from the University of Wisconsin (UW) and experienced clinician-investigators from our hub will co-develop a mentor training curriculum for 24-30 clinician/clinical trialist mentors. The anticipated 4-hour curriculum will cover 6 standard core competencies along with elements from the Enhancing Cultural Awareness curriculum and a newly developed workshop on team mentoring, and will be offered in-person at one study site and virtually at the other so as to enable comparing modalities. Clinicians completing the mentor training will then be matched to current K12 Scholars and join their mentorship teams. The clinician mentor will advise the Scholar regarding feasibility of conducting clinical research projects, translating research findings into clinical practice, and other matters as they arise. A mixed-methods evaluation will assess the experiences of clinician mentors and K12 Scholars once they have worked together. To sustain the program beyond the grant award period, using their train-the-trainer model, the UW team will train a UTHSCSA CTSA hub co-investigator to administer the training. We will disseminate the curriculum through the national KL2/K12 PI Directors Consortium Group; the recently launched CTSA Mentorship Community of Practice led by UW; conference presentations; and publications. Although the proposed clinician mentor training is designed to fill the needs of K12 Scholars locally and nationally, other trainees, such as predoctoral and postdoctoral T32 trainees, and junior faculty conducting CTS stand to benefit as well.