This paper describes the development and validation of an instrument for measuring learner perception of pedagogical agent persona. After collating items from other empirical studies, exploratory and confirmatory factor analyses were conducted with three samples of undergraduate students working within the Multiple Intelligent Mentors Instructing Collaboratively (MIMIC) agent-based research environment. The final model identified four pedagogical agent persona factors (Credible, Facilitating Learning, Engaging, and Human-like) and two latent variables (Informational Usefulness and Affective Interaction). Results suggest that there are two primary aspects to student perception of a pedagogical agent’s persona: 1) its role as a knowledgeable instructor that facilitates learning; and, 2) its provision of affective, human-like interactions in the process. The final model is discussed with respect to its implications for pedagogical agent research and computer-based instructor characteristics.