Abstract: Vulnerable persons are thosewho are relatively (or absolutely) incapable of protecting their own interests.More formally, they may have insufficient power, intelligence, education, resources, strength, or other needed attributes to protect their own interests.Special justification is required for inviting vulnerable individuals to serve as research subjects and, if they are selected, the means of protecting their rights and welfare must be strictly applied.This article focuses on the international ethical requirements of biomedical research involving children, individuals who by reason of mental or behavioral disorders are not capable of giving adequately informed consent, women, and pregnant women, etc.Finally, it talks about the duality of research, i.e, burden and benefits.No groups and individuals, including vulnerable groups should bear more than its fair share of the burdens of participation in research.Similarly, no group should be deprived of its fair share of the benefits of research.

Key words: medical ethics, clinical trial, Council for International Organizations of Medical Sciences, guideline, ethical, vulnerable groups