Humans are considered the noblest being in the world. Due to its one-time and sacred attributes, the right to life should be protected the most among other rights. Prior to law, life is a given. It is something with the noblest value that cannot be exchanged with anything. No one is allowed to dispose it. Thus, the right to life should be defended as a pillar of human dignity, in line with the right to lead a humane life in the Constitution and the dignity of life. As bio medicine has advanced, IVF, abortion, and human cloning were made possible. Such advances in medical equipment and skills extended life span that otherwise would have died. Along with it, the matter of ethics has emerged. Terminal patients, in fact, have to suffer from illnesses as well as unwanted life extension. In addition, their families have to endure financial, physical and emotional burdens. To relieve such burden, the introduction of euthanasia has been discussed. Euthanasia a matter of balance between the dignity of life and the termination of life that is suffering physical pains. There are two different types of euthanasia such as sedative euthanasia, indirect euthanasia, active euthanasia, passive euthanasia (end of life support). There is a consensus on sedative euthanasia and indirect euthanasia. Therefore, this paper explored the conditions of legalization, focusing on active euthanasia and the termination of treatment which would quicken a death. Mercy killing by the termination of treatment is allowed as long as it is compatible with the patient's articulation of the intention or presumptive intention. It is because doctors' duty and guarantor's status have been removed by a patient's intention. Yet, when a patient is incapable of articulating his intention, the patient's intention should be presumed. Even when the presumption is unavailable, the decision to terminate treatment has to be made based on objective standards. There are several criteria for the decision. In the case of irrevocable unconsciousness when a patient is diagnosed that he completely lost consciousness with little hope of recovering, it is appropriate to see the limits of doctors' duty of life support as objective criteria. Therefore, euthanasia by the termination of treatment is allowed in the case of the irrevocable unconsciousness. Yet, before reaching the irrevocable nconsciousness, doctors' bear the duty of life support and euthanasia is not allowed. On the other hand, active euthanasia should not be allowed even with a patient's request or approval. It is widely held that even active euthanasia does not constitute illegality if it is executed under specific conditions, based on that it is not against established social rules. Still, the specific conditions are not defined since they are expressed in abstract terms. Moreover, there is a possibilityof abuse. It cannot be justified since it infringes on the forbiddance of murder in that it quickens a death without trying to alleviating or removing pains. In the liability exemption, it would not be appropriate to decide to quicken a death by relying on an actor's psychology in the legal interests. Therefore, active euthanasia constitutes a murder by request or approval, stipulated in the 1st clause of the 252nd article, even though it was at the articulation of a patient's intention. Without a patient's intention, it constitutes a murder in the 250th article. The conditions of legalization of euthanasia do not include active euthanasia. Euthanasia by the termination of treatment is determined according to a patient's right to decision. Euthanasia is allowed as long as it is in line with a patient's articulation or presumptive intention. When a patient is incapable of articulate his intention, irrevocable unconsciousness should the only condition for euthanasia. As shown in laws and precedents of other countries, different conclusions are drawn according to the times and their philosophies. While Dr. Kevorkian was guilty to a felony in the US, he would have been innocent in the Netherlands. There are no uniform criteria or conditions for euthanasia. In additions, a single country so far had clearly taken the stand of either pro or con. Therefore, in terms of the legalization of euthanasia, it is not appropriate for Korea to keep up with the trends when euthanasia is not covered by medical benefits. It is recommendable that the matter of euthanasia should be resolved according to penal theories unless it is to shorten the precious life of humans.