Due to the lack of valid measurement for measuring national competitive- ness (CN), some shortcomings of IMD's "World Competitiveness Report," and the need to disclose the comparative CN between Taiwan and Mainland China, this study follows Chen & Tarn's (1997), which pays effort to the measurement of CN, to measure Porter's (1990) "Diamond," and the modified "Double Diamond." With the guidance from three scholars and 12 practitioners, a five-determinants, 12- construct, 31-item scale is built. The 103-observation empirical evidence shows good convergent validity and moderate discriminate validity for the new scale. This study selects the "Giving-Taking Level" of Taiwan-owned firms that operate in Mainland China (TFCs) as criterion, and lists moderate criterion validity. The results also show that TFCs "give" too much to but "take" less from mainland, and Taiwan is more competitive than mainland, especially on the related and supporting industries, and strategic capability owned by the business. Some discussions and future directions are also pointed out.