As the number of clinical trials in Korea has been increasing in recent years, the public start having concerns about the protection of human subjects in research. The ethical aspect of clinical trials is considered as one of the most important issues, and informed consent lies in the core of the ethical conduct of clinical research. Informed consent requires three key components to be ethically valid: information, comprehension and voluntariness. Furthermore, the consent process should be properly executed to ensure that the circumstances in which consent is obtained are free of coercion and undue influence. There are lots of challenges to conducting proper informed consent. The purpose of this article was to describe those challenges and to provide suggestions for improving informed consent.