The "Disposition Effect" indicates that investors in the stock markets tend to sell to realize the profit as they are "in the money", and hold securities to avoid loss as they are "out of the money". Similar investors' behaviors in the real estate markets are rarely explored. In Taiwan, continuously surging home prices have severely deteriorated home affordability. Underlying factors causing the high housing prices include low tax rate and low interest rates. To analyze investor behavior in the housing markets, this study analyzes the transaction volume in the existing housing market in relation to market return. The empirical results show that investors in the existing housing markets tend to sell to realize profits as the returns stay positive or turn from negative to positive. However, investors tend to hold to avoid loss as the returns stay negative. This conclusion is consistent with the investor behavior of stock markets. The analytical results of this study also imply that the "Luxury Tax" imposed on short-term real estate investment only postpones their timing to sell. However, housing prices continue to appreciate. Results of this study have important implications for policy makers and investors for decision making in the future.