The article 128 of the Patent Act in Korea stipulates the provision on the calculation of damages. However, discussions have continued to see if this provision enables the patent right holder to calculate proper damages. and increasing number of arguments have been raised continually that the damages must be higher than now in the calculation of damages caused by patent infringement. So far, the calculated damages caused by patent infringement under the current patent act are very low compared with other countries such as the US and the amount has been calculated considerably lower than actual claimed amount. Accordingly, this study aimed to explain the method of calculation of damages by patent infringement in major countries, to review the provisions in the Article 128 of the Patent Act, to discuss problems of applying those provisions and then to review required efforts for the calculation of proper damages.