This paper describes the construction method and investment performance of the Taiwan Sustainability Index (TWNSI). The National Taipei University Corporate Sustainability Research Team and the Taiwan Institute for Sustainable Energy (TAISE) adhere to two purposes to jointly construct TWNSI: 1. to enhance the long-term investment performance, and 2. to promote the concept of corporate social responsibility (CSR). It is hoped that through the construction of TWNSI, companies with outstanding sustainable performances will be selected not only for investors who want to achieve good investment performance and at the same time to support those good companies, but also to promote the fund allocation efficiency in Taiwan’s stock market. The criteria for constructing TWNSI include (1) financial performance guidelines, which include company’s financial performance and stock market quality; and (2) sustainable performance criteria, which include the facets of social, environmental, economic, and disclosure (SEED). In January 2019, TWNSI was assured by the German index company, Solactive, and was officially launched on Reuters and Bloomberg, respectively. The backtesting performance reveal that TWNSI’s half-year, one-year, two-year, three-year, five-year, and 10-year return rates, as well as indices such as Jensen’s alpha, Treynor’s Index, and Sharpe’s Index, all significantly outperform the Taiwan 50 Index, Taiwan stock market, and the FTSE4good Tip Taiwan ESG Index.