The present invention relates to a method of preparing a metal oxide-silica composite aerogel and a metal oxide-silica composite aerogel having an excellent weight reduction property prepared by the method. More particularly, the present invention relates to a method of preparing a metal oxide-silica composite aerogel, the method including a step of adding an acid catalyst to a first water glass solution to prepare an acidic water glass solution (step 1); a step of adding a metal ion solution to the acidic water glass solution to prepare a precursor solution (step 2); and a step of adding a second water glass solution to the precursor solution and performing a gelation reaction (step 3), wherein, in steps 2 and 3, bubbling is performed with an inert gas.