The development of clinical competencies in psychology requires real and simulated interactions, leading to the use of several assessment methods such as the Objective Structured Clinical Examination (OSCE). One of the basic clinical intervention techniques is the motivational interview. The use of OSCE in psychological clinical simulation lacks publications regarding its use in undergraduate students. The purpose of this study is to describe the use of the OSCE as a tool for the assessment of two clinical competencies: patient relationship and motivational interviewing. The participants were undergraduate students of Clinical and Health Psychology of Tecnológico de Monterrey, México 95.74% female gender. The census sample was N1 = 47 (pretest) and N2 = 46 (post-test). The study design was descriptive with a quantitative approach, using a checklist, applied before and after their clinical rotations (960 h of supervised practice distributed over one year, in hospital environments and community care clinics). The pretest results indicate 77% of the students demonstrated adequate skills in motivational interviewing and the post-test showed 82% improvement in the domain of motivational interviewing as a clinical tool, especially the elements of the empathic reaction with the patient and the initial setting of the interview. The implications of this study for clinical psychology education and practice are to design curricular activities as well as to guidelines in clinical supervision.