Based on the case-method, an exercise using debate is proposed for practical education in engineering ethics. The exercise is performed as a group-work composed of discussion and debate. This paper describes design concepts and discusses the methodology of the group-work for enhancing educational effects based on the result of a questionnaire. The author proposes a feasible model plan for implementation of two debates in 90-minute class : five minutes allotted for constructive and rebuttal speeches, four minutes for cross examinations, and eight minutes for preparation time. The adequate number of group members and the minimum required time of discussion are also proposed.