Physical vapor deposition(PVD) techniques offer a means of depositing refractory materials onto polymeric substrates at low temperature as well as the advantage of performing accurately controllable deposition. Ceramic coatings deposited on polymers are suitable in packaging applications where high gas-barrier properties are needed. The purpose of this work is to investigate some of the basic properties of sputtered aluminum oxide thin films and to show their dependence on the plasma time and the rf power. the aluminum oxide thin films have been deposited in PET substrate film using rf magnetron sputtering from an aluminum oxide magnetron target and argon plasma.