In the conventional WWW-based CAI, the students just see or read the object passively, so it is hard to master the subject. The authors therefore pay attention to the educational theory of ``Learning by Teaching¡Ç¡Ç for more effective learning. The theory of ``Learning by Teaching¡Ç¡Ç is that when the learner teaches others actively and the responses from others be fed bak to himself, he can learn more deeply by thinking and self-examining. So we constructed the conversational WWW-base CAI system with personified agent applying this theory. The CAI system provides a new system function of teaching to the personified agent ``Virtual Agent¡Ç¡Ç as a character. Through the interaction with Virtual Student, the student can promote his learning. And then, we conducted the laboratory experiment in order to evaluate this CAI system. In this experiment, so as to evaluate its effecctiveness objectively we conducted achievement test and to examine its factors we did the questionnaire survey. Therefore, it was confirmed that this CAI system was effective for learning.