In this monograph econometric analysis of the portfolio behavior of the Ethiopian Commercial Banking Sector has been done. More particularly, the portfolio behavior of Defensive Assets, Treasury Bills, Loans, Long-term Securities, Deposits & Bank Capital has been thoroughly studied. It is strongly believed the study contributed a lot to the existing stock of knowledge related to the portfolio behavior of banks in developing countries. While adopting a critical and perceptive attitude through a good literature survey and empirical work, significant attempt has been made to show the different possible relationships of the investigation to the wider context of knowledge in which it belongs. The empirical findings of the thesis are believed to be useful to a wider audience covering from academics to policy makers.