The issue of judging inventive step in the proceedings of both patent prosecution and litigation has been one of the most challenging tasks. It is a crucial legal issue in the patent practice in Taiwan as it is unavoidable in most of the cases. The patent law can provide little guidance to judge the issue of inventive step because of the laws abstraction nature. The practice of the US and Germany heavily rely on the methodology generated by the case law to solve the issue. Their methodology works quite well and that the methodology of the US and Germany are surprisingly similar after comparing the case law in the two regions. The intention of this article is to introduce the US and the Germany the methodology with respect to judging inventive step on the basis of its case law and use it to review the Taiwanese practice. The key point of the recommended methodology is to focus on the subjective knowledge of the skilled in the art, not like the current Taiwanese case law which pays too much attention to the objective difference between the patent and prior art references. By properly applying the subjective rule may help correct the current difficulty facing in Taiwan that over 60% invention patents asserted in the patent litigation are held to be invalid.