This essay aims to review the rationale of sentencing in Korean criminal laws and procedures to understand how to secure rational sentencing with the rationales of sentencing, such as responsibility of offenders and general deterrence or specific deterrence. Shuldprinzip or principle of responsibility is the fundamental basis of criminal punishment, which also acknowledged as constitutional principle for criminal laws. However, Korean Penal Code has no definite provisions on the purpose(s) of punishment or sentencing. Considering such statutory definition of the rationale is necessary for rationalizing sentencing discretion, Article 51 of the Penal Code is the only relevant provision on some ‘general principles’ of sentencing : In determining punishment, the following shall be taken into consideration: 1. The age, character and conduct, intelligence and environment of the offender; 2. Offender's relation to the victim; 3. The motive for the commission of the crime, the means and the result; 4. Circumstances after the commission of the crime. Also, Korean sentencing guideline system under the Court Organization Act has set some principles of setting or changing the sentencing criteria: 1. The nature of crimes, the circumstances of crimes, and the extent of the responsibilities of defendants shall be reflected; 2. The general deterrence, the prevention of defendants from committing crimes again and their return to society shall be taken consideration; 3. As long as there is no difference between the same kind of crimes and the similar kind of crimes in the sentencing elements that have to be taken into account, they shall not be differently handled in the sentencing of them; 4. The sentencing shall not be discriminated against defendants on the grounds of their nationalities, religions, conscience, social statuses, etc. (Article 81-6(2)) Now the sentencing guideline system is taking the role of rationalizing sentencing discretion by both reflecting responsibilities of defendants and considering the general deterrence of crimes or the prevention of defendants from re-offending and their rehabilitation, and further realizing the purposed of just punishment. According to the law, when setting and changing the sentencing guidelines, the guidelines should reflect the degree of responsibility of the defendant, and consider the general prevention of crime and the prevention of recidivism and social rehabilitation of the defendant. So for the rationalization of sentencing, it should be possible to make sentencing-policy judgments on responsibility and prevention considerations through the principles of responsibility and prevention considerations rather than unclear normative adjustments of sentencing guidelines.