A method for actuating a piezoelectric actuator and a piezo injector of a fuel injection system having a nozzle needle which can be moved between the closed position and an open position by the piezoelectric actuator are disclosed. Current is applied to the piezoelectric actuator from a source for the duration of a charging time as a function of a required quantity of fuel, in order to move the nozzle needle into its opened position for a time period which is dependent on the required quantity of fuel. The charging time is selected according to the following relationships: tcharge(p)=tnom,charge (p) for TI>tEP,p and tcharge (p, TI)≦Ti for TI≦tEP,p.