Given the importance of the motivational climate in Physical Education, this paper presents the process of design and validation of an instrument of “Observation of the Motivational Interpersonal Climate (OCIM)” for Physical Education teachers. This instrument based on the Self-determination Theory has followed the principles established in the observational methodology. A bibliographic search and an analysis of the observation instruments to date about the motivational climate was carried out to create the OCIM. The tool ad hoc has been designed using a mixed system of field format and a system of categories mutually exclusive. The results obtained through the Kappa indices and the Generalizability Theory have shown satisfactory reliability and different evidence of validity. The OCIM allows to know the degree in which teachers support or controlling the Basic Psychological Needs (including Novelty) and orienting the interpersonal motivational climate towards the autonomy-supportive or controlling style.