The purpose of this study is to investigate the factors which drive institutional investors’ investment decisions in Taiwan ETFs market. The thesis first predicts phases of the financial cycle in a Markov switching framework. VIX index is used to identify the turning points for a transition to a volatile state. The state variable, other institutional investors’ investment behavior in ETFs, and investor's sentiment variables are then use to explain the behaviors of three major institutional investors’ ETF shares in a vector autoregressive (VAR) framework. In particular, the study asks the following two research questions: (1) Whether institutional investors will invest in different types of ETFs in various financial market states, and (2) Whether there will be any interactions among the three types of major institutional investors in their ETF investment. Understanding the institutional investor behavior can help investment trust companies to promote ETFs in various financial states.