Deposit mobilization is a fundamental part of banking activity. (Banson, et al, 2012), well-rndefined that “mobilization of deposit for a bank is as essential as oxygen for human being†andrn“Deposits are the life blood of banking companiesâ€. Hence, deposit mobilization is critical tornBanks. The research tried to determine factors that affect deposit mobilization, the associatedrncosts of deposit mobilization in private banks. Therefore, the study adopts mixed approach torngather the data. The primary data is gathered using questionnaire. Sampling method of thernprimary data is purposive sampling technique. While the secondary sources of data werernextracted from annual reports of all private commercial banks of Ethiopia, data from NationalrnBank of Ethiopia (NBE) and from Central Statistical Authority (CSA). Regarding the secondaryrndata, the study used time series data from 2000-2014 for analysis made using Classical linearrnregression method. The study shows that, Age dependency ratio, Investment and money supply,rnare the most significant factors of deposit mobilization activity. The other variable such as Perrncapita income has insignificant power to influence the dependent variable. As a result, the studyrnrecommended that, Government should increase investment so as to promote economic growthrnto mobilize deposits since there exists a positive relationship between Deposit and Investment.rnAnd private banks ought to increase number of branches to mobilize more resources