Emerging technologies are playing an important role in establishing competitive advantage for technology based companies. Selecting an efficient and important emerging technology to invest in is significant to the companies also. In this study, we propose a method for selecting optimal emerging technology which is efficient, important and the most suitable to a company’s actual levels of input resource among various emerging technology alternatives. In order to select optimal emerging technology, the proposed method uses two-level-SOM to cluster the emerging technology alternatives based on alternatives’ required levels of input resource. For selecting efficient and important promising emerging technology, the proposed method calculates emerging technology alternatives’ efficiency score by using AHP/DEAAR and their importance score by using AHP rating method in each technology cluster generated by two-level-SOM. Finally, the proposed method selects optimal promising emerging technology according to a company’s actual levels of input resource and each emerging technology alternative’s combined scores which is calculated by adding its efficiency score and importance score. A Korean company’s case of selecting optimal promising nanotechnology is employed to illustrate the proposed method. The result shows that the proposed method can provide an effective and reasonable selection of optimal promising emerging technology