The purposes of this study are to confirm the standard of ethical judgement ability of the mathematically gifted students and examine which factor makes on the ethical judgement ability among the mathematically behavior characteristics. For it, correlation analysis and regression analysis between the two things were conducted with SPSS 12.0 based on the results of mathematically behavior characteristic inspection and ethical judgement ability inspection. Also, the interview was conducted for students whose KDIT score is the highest and the results were intended to apply the results as the material supporting the results of qualitative test results. The interview with students examined which mathematically behavior characteristic factor made an effect on his own ethical judgement ability through the structural questionnaires.