The present study was intended to comprehensively review legal and ethical considerations for special classes of subjects to protect human research subjects and to suggest the several issues about studying the human subjects. According to development and innovation of biomedical sciences, the necessity of involving human subjects such as fetus, pregnent woman, children and minors, cognitively impaired persons, prisoners, traumatized and comatous patients, terminally ill patients, minorities, students, employees and normal volunteer in research is clear. Without their participation, progress in the understanding and accumulation of knowledge in these areaes will be stifled. However, because of there is few regulations and legal devices about evaluation of research, many questions and confusion about bioethics was arised. Especially, careful consideration and evaluation of legitimacy, safety and importance of research involving human subject is needed at the present time. If the risks of research involving human subject exceed the level considered minimal, the researchers must be justified by anticipated benefit for the health of the human subject. Therefore, the authors suggest that more criterias which can evaluate the legitimacy of the research are needed and the development and initiation of regulation and organization such as national commission for the protection of human sunjects are required. Finally, the author recommended that the curriculum about bioethics for research in graduate or postgraduate courses is fortified for preparation of researcher of future society. Ethical considerations call upon investigators to maintain the dignity of human subject and ta avoid unseemly intrusions for research purpose.