Abstract-The purpose of this study was to develop "Chemtective" as a game-based learning medium which was valid, practical, and effective in improving students' interest and motivation in learning Chemistry. "Chemtective" is a computer game-based medium designed by collaborating "chemistry subject" and "detective stories". The method employed in this study was Research and Development (R & D). The validity of the medium was evaluated by three media experts. As many as 34 students of SMA Negeri 2 Banjarmasin were selected as the try out subjects. The data of validity, practicality and effectiveness of the medium were collected by using validity sheet, observation sheet, students' responses and students' interest questionnaire. The practicality of the medium was evaluated by three observers and the effectiveness was evidenced by the improvement of students' interest in learning chemistry. The analysis of the data used percentage method. The result showed that "Chemtective" was valid, can practically be implemented, and was effective to improve students' interest in learning chemistry.