Supreme Court of Korea has been mitigating the burden of proof on the malpractice and causal relation by a patient in accordance with the practical transfer of such burden of proof on causal relation as well as relieving a doctor's burden of proof on mistake in the civil damage claim suits on the malpractice. However, a prosecutor shall strictly prove the causal relation between malpractice and unfavorable results as well as a doctor's mistake in the criminal cases for making a doctor accept the professional negligence resulting in death or injury in accordance with In Dubio Pro Reo principles. Furthermore, it shall not be allowed to relieve the burden of proof on malpractice and causal relation which has been frequently applied in the civil proceedings. Nevertheless, it was widely known that the front-line courts accepted the malpractice and causal relation by quoting the legal principles on relieving the burden of proof on malpractice and causal relation applied in the civil cases even in criminal cases with no or insufficient proof on malpractice or causal relation. However, the latest precedents in Supreme Court explicitly declared the opinion that there was no reason to apply the legal principle to relieve the burden of proof on the malpractice and causal relation in the criminal cases requiring the proof 'which doesn't cause any reasonable doubt' on malpractice and causal relation in accordance with the legal principles 'favorable judgment for a defendant in case of any doubt' on the basis of the strict principle of 'nulla poena sine lege.' Accordingly, Supreme court definitely clarified that there would be no reason to relieve the burden of proof on malpractice and causal relation in criminal cases by reversing several original judgments accepting malpractice and causal relation even though there were no strict evidence.