This paper presents a study of a Student Model based on beliefs of Self-Efficacy to improve the effectiveness of Intelligent E-Learning System. The Self-efficacy means the student?s belief on his capacity of performing a task. This belief affects his behavior, motivation, affectivity and the choices he makes. We design an e-Learning System, called InteliWeb, this environment is composed by the Self-Efficacy Mediator Agent, an animated pedagogical agent and offers instruction material on Biological sciences. We use fuzzy theory for dealing with uncertainty in the assessment of the students and the incomplete knowledge about his Self-Efficacy.