Housing investment plays a vital role in the real estate market. Although the housing investment has been extensively investigated, the application of Tobin¡¦s Q theory is relatively minor. Hence, the purpose of this study is to apply Tobin¡¦s Q theory to analyze housing investment, using quarterly data for Taipei City from 1973 Q2 to 2010 Q4. The Q ratio numerator is the pre-sale housing price and the denominator represents the value of the rent. The empirical model is estimated by using building permits and use permits as measures of housing investment. Moreover, because the housing market is imperfect, this study applies the threshold regression model to test whether different effects exist in the Q ratio. Finally, this study also compares housing investment in five cities. In conclusion, these findings imply that the Q ratio has a positive relationship with housing investment, as well as a threshold effect. Furthermore, the local housing investments are affected differently by local variables.