Endocrine System in Human Beings' is one of the most difficult subjects for students although they regard it as a subject connected with real life(Zohre, 1999; Saka, 2001). In the studies carried out on the subject, it was found that high school students had wrong ideas about the transfer of hormones to target organs, which was in the subject of endocrine glands, and they could not explain the function of hormones in the feedback mechanism(zahre, 1999). Saka(2001) confirmed that high school students could not show the endocrine system glands on human body. In the study by Zohre(1999), teachers stated that students' interest in the endocrine system subjects was low and their success in the endocrine system subject was lower when compared with other subjects. In the shidy, teachers were also found to be in need of visual materials related with the subject, which had a compact and abstract content. Within the content of the current study, a computer assisted problem based leaming environment which requires that students use their high level skills such as research questioning, deep thinking, reflecting and problem solving was developed in the subject of Endocrine System in Human Beings' in accordance with the 303R model and was introduced Below is the information on the 3C3R model, which the CAPBL environment was based on