The California State University, Long Beach (CSULB) BUILDing Infrastructure Leading to Diversity (BUILD) program developed a near-peer mentoring component in which master's students serve as mentors for undergraduate research trainees in health-related disciplines, in addition to fulfilling teaching assistant duties. This paper has two parts. The first describes (a) the functions of this mentoring component, taking into consideration the context of CSULB; (b) the extensive year-round training curriculum for near-peer mentors; and (c) the evolution of this curriculum in response to feedback from BUILD trainees, near-peer mentors, and undergraduate research training instructors. The second part evaluates the effectiveness of the near-peer mentoring component, based on focus groups and quantitative surveys of both near-peer mentors and mentees. We offer recommendations for master's comprehensive research institutions interested in implementing near-peer mentoring within similar research training programs.