Intangible assets are the important tool which decides upon economic wealth and development of knowledge-information economy. We have to make effective use of intangible assets in order to assure surplus earnings, competitive superiority. The importance of intangible assets, especially patent right, may be properly understood only when their values are assessed adequately. It is very significant to appraise rationally patent right value from finance support, technology transaction, investment decision, M&A, legal proceedings, strategy and etc. Thus the purpose of this study is to evaluate the economic value of a patent right using DCF(Discounted-Cash Flow Method). This paper presents the basic model, related principles and standards of valuation, and then, case analysis of patent right valuation using DCF.